By Bob Goemans
Site Supported in Part by:

The 'LIVING' Marine Aquarium Manual

Basic and Advanced Husbandry for the 'Modern' Marine Aquarium

by Bob Goemans

Chapter 12 – Algae: the Good, Bad, and Ugly

Now with the system goal chosen, necessary equipment purchased to establish it, and well armed with system filtration techniques and seawater generalities, the next logical step is to explore what that system will need in on-going maintenance to remain a healthy environment for its inhabitants.

Lets first concentrate on 'algae' because without an understanding of what generates algae growth, no system is protected from what can easily turn into a disaster. In fact the topic is so important that I'm dedicating an entire chapter to it. Furthermore, there may be some repeats of previous discussed topics here and there throughout this chapter but consider it necessary to bring home the information needed to thoroughly voice my thoughts on these topics.

(Please keep in mind all underlined word(s) are linkable files - just click on them and be taken to its content/photo. Also, all shown photos are clickable, which often allows a larger file to be seen.)

In the seventies and early eighties most aquarists considered healthy growths of micro or macroalgae an indicator of good water quality. In some ways that was appropriate thinking, yet it's quite possible those growths may have become a major annoyance. In fact, there's no doubt that excessive growths of unwanted forms of algae have caused some aquarists to leave the hobby in total disgust.

Most aquarists realize it's difficult to find algae on the reef in the wild, yet there's always some calcareous and/or turf algae because they are actually important building components of any natural reef system. But with the reef's surrounding water nutrient poor and herbivores keeping what there is of algae well mowed, little or none is readily visible. Nevertheless it's another story in shallow inland waterways and bays where nutrients have a tendency to accumulate. There, algae in various forms and amounts can easily be seen and it's these types of algae that present the most problems for many aquarists.

As mentioned above I can remember when a good growth of any kind of green algae in a marine aquarium was time for smiles. That's no longer totally true in many marine aquariums, especially in reef aquariums. Only calcareous algae such as Halimeda or Coralline, or possibly a controlled growth of Caulerpa is considered acceptable. Filamentous or slime-like growths are almost always considered problematic and usually become costly in time and money to remedy.

There are also various colors of algae in aquariums, e.g., green, brown, and red, and can be single-cell, multicellular, encrusting, slime-like, or plant-like in appearance. Some perform beneficial functions such as the production of oxygen and the removal of various toxic compounds, while others can be harmful to fishes and coral. To promote conditions in closed systems that compliment only the more beneficial forms of algae, it needs to be discussed in a thorough and easily understood manner. That's difficult because there are many contributing factors, types of algae, and misconceptions surrounding the subject matter. However it's my goal here, so lets begin with 'Beneficial Species' and go from there.

Beneficial Species

There are many forms of algae; no matter what their color, that serve useful purposes. Those could be a food source; decorative purpose; inhabitant shelter; or a means to export nutrients such as those used in refugia or alga turf filters. It would be far beyond the scope of this book to name all the species that can show up in aquaria or in the trade. However, I'll discuss the more commonly seen species in relation to what's the most beneficial in this topic and in the 'Unwanted' topic below discuss those species that have the potential to create problems in the aquarium and/or give some aquarists gray hair!

One of the most advantageous reasons for maintaining some species of algae in aquarium is their photosynthesis process uses carbon dioxide and in turn provides oxygen for the aquarium animals. This also helps raise system pH and increase system carbonate buffer capacity (alkalinity). They also help to remove unwanted compounds such as ammonium, nitrate and some heavy metals from the bulk water. Keep in mind the nitrate removed is broken down by internal enzymes, similar to reverse denitrification, until the ammonium needed for growth is attained. Removing or pruning back older growth serves as a way to export the absorbed unwanted nutrients.

There is even a somewhat beneficial side to some forms of cyanobacteria. And you thought it was all bad! Well, you're almost right, but not 100%. Cyanobacteria is an early colonizer of substrates and an indicator the microbial biomass is progressing. How far these growths should be allowed to progress is discussed further on in this chapter.

As for more desirable forms of algae, there is some of particular interest to aquarists. It's these species to concentrate on, and if properly controlled lend themselves to improving system environment and water quality. However, even with the more desirable species, if not properly maintained they can lead to throwing in the towel so to speak!


This green, terrestrial plant-like and multi-shaped macroalgae is probably the most popular. It can be found readily available at most marine aquarium shops, and there are about seventy different species with many prolific growers. Root-like holdfasts grow along their rhizomes and attach themselves to substrate, rock, and even coral animals. The main purpose of these growths is to anchor the plant to a substrate surface, yet some uptake of nutrients is thought possible. However, the majority of nutrient uptake is through the fron/leaf surface.

Caulerpa are coenocytes, i.e., a multinucleate cytoplasm appearing as many interconnected segments. The proper way to break off a section of this type alga is to crush the thallus (stem) between the plant-like leaf structures, not make a clean cut such as with a scissors. Clean cuts can lead to internal damage and quickly cause a section or the entire specimen to disintegrate. Beside disintegration from physical abuse, cellophaning, i.e., becoming transparent, can be caused by sexual reproduction. When this occurs, the Caulerpa leaf will first become blotchy. Soon after blotchyness appears, hair-like discharge tubes called 'papillae' will form along the edges of the leaves and discharge gametes and some remaining cytoplasm.

There are some thoughts as to why Caulerpa enter the sexual cycle. Some think it is brought about by salinity changes. Some think it may simply be a biological clock, while others think it may be brought about by a lack of nutrients, e.g., carbon dioxide, nitrate, iron or that of excess organic material. No matter what the cause, when Caulerpa begins to cellophane, those leaves should be removed before disintegrating altogether. If allowed to disintegrate, the plant's nutrients will be released into the aquarium, reducing overall bulk water quality. Generally, excellent growths of Caulerpa can be maintained by simply harvesting the oldest one-third of growth as necessary.

Caulerpa, as with most algae, do better under regular daylight fluorescent lamps than under more expensive blue spectrum lamps such as 6500 or 10,000+ Kelvin lamps. The reason for this is that algae prefer longer wavelength light, such as the red band wavelength. Higher Kelvin rated lamps have a blue-green spectrum, which algae do not find as useful as the red band. Caulerpa also prefer what could be termed average water conditions, i.e., where nutrients such as ammonium, nitrate, and phosphate are somewhat available.

In fact, I could not get macroalgae to grow in a plenum-equipped system where nitrate was constantly below 3 ppm nitrate-nitrogen (NO3-N). Every time I tried a new specimen it would cellophane and die. As an experiment I carefully split a specimen, C. prolifera and added half to another aquarium. This other aquarium had a sandbed directly on its bottom and its temperature and salinity were the same as the plenum-equipped aquarium. The specimen in the aquarium with the sandbed directly on its bottom grew well. The major difference between the two aquariums was that the one with sand directly on its bottom had a nitrate level of 8 ppm. As I brought down its nitrate level, Caulerpa growth slowed. Under 3 ppm, growth stopped and the specimen began to cellophane.

Some aquarists refer to Caulerpa as a pest because it can block light or its holdfasts annoy corals. Preventing this type stress is a simple matter of guiding new growth away from coral animals. It is also known that Caulerpa release a toxin called Caulerpicin, which may inhibit coral growth and possibly harm some fishes. Caulerpicin and organic leachates that yellow bulk water can be removed with adequate protein skimming and/or proper use of activated carbon.

Some Caulerpa species are a favorite of herbivorous fishes such as Tangs. Notice I said 'some' as I've found only two species, C. mexicana and C. prolifera that are usually eaten with relish (No, not that kind of relish!). The following four are generally more of interest:

C. mexicana - Its bright green feather-like growth is the best of all the Caulerpa species for aquarium use. Leaf/fron/blade length varies, yet is usually 6 - 8 inches (15 - 20 cm). The oppositely arranged, segmented points face upward on a basically flat-shaped leaf. The leaves are attached to and are spread by rhizomes/runners, which in turn are held in place by holdfasts/rootlets. This form of Caulerpa releases fewer toxins than other types of Caulerpa and fish such as Tangs find it quite tasty. In fact, this species and C. prolifera are the only two Caulerpa species usually eaten by most herbivorous fishes. It is usually referred to as 'fern' macroalgae and makes for a very good foodstuff for many different kinds of herbivores.

C. prolifera - Grows similar to C. mexicana, yet has a flat non-segmented tape-like and vertical, slightly curled leaf. The leaf length varies, usually 4 - 8 inches (10 - 20 cm). Sometimes a second leaf will start growing from the main leaf. Most herbivores will eat it. However it's prone to sexual reproduction disintegration if not diligently pruned.

C. racemosa - This light green vine-like Caulerpa has bunches of miniature grape-like beads intertwined on short and low growing branchlets, and forms spreading carpets. The grapes or spheres range in size from 1 - 3 mm. Most fish do not seem to like its taste, yet have seen Tangs eating it occasionally. It is usually referred to as 'Grape' macroalgae and this particular species and the one below are highly recommended for lighted refugia where rapid plant growth and nutrient export is beneficial.

C. sertularioides – Has small upright blades, about 1 – 2 inches (2 – 5 cm) containing saw-like edges that are often 'Y' shaped and growing along the runners (rhizomes). Its one of the more prolific species and considered one of the better refugia species because of its abundant growth and being less prone to sexual reproduction disintegration. Another would be C. taxifolia (considered an invasive species as it has overrun various areas in the wild) and possibly C. floridana.

Refugium Alga

Another excellent and very fast growing macroalgae is Chaetomorpha linium. Its course, wire-like strands can be found in a variety of forms/other species, from simple hair like growths to woven masses. For refugia and/or alga turf filters its an excellent algae for nutrient export and the species shown here can be simply floated in refugia with no substrate, which makes it quite easy to keep its bottom area clean of settling detritus/less overall system nutrients. And maybe best of all, it can be lit by common household fluorescent lamps, as they best suit it because these lamps have a higher red spectrum content, something all algae prefer.

Calcareous Algae

Upright growing forms of calcareous algae contain a large amount of calcium that provides a certain amount of stiffness. Growth rate depends upon the availability of calcium, magnesium and trace amounts of iron and iodine as iodide. Under the right circumstances, some forms of calcareous algae can grow as much as a few inches per day. There are numerous species, but the following green species are more common and generally available:

Halimeda opuntia - Shaped like a prickly pear cactus and sometimes called Cactus Algae or Money Plant, it prefers medium to indirect light. Besides needing a calcium level near that of NSW, about 400 ppm, it appears to do better if alkalinity is maintained between 3.5 - 4.5 meq/l or even slightly higher. When this alkalinity range is maintained I have seen this dark green plant grow in my aquariums at a rate of 0.25 inch (.6 cm) per day. It's a good species for aquariums with grazers such as Tangs because the calcareous makeup of the plant helps keep their digestive system free of blockages. Halimeda discoidea, and Halimeda incrassata are another two favorites.

Penicillus dumetosus and Penicillus capitatus - Referred to as Neptune's Shaving Brush because they have a thick stalk crowned with a tuft of green to white filaments. Prefers sandy bottom areas and intense light and has the same water quality requirements as Halimeda opuntia. Its upright stalks are short lived however, maybe lasting only a few weeks. Yet new growths will occur within a short distance of the main stalk via runners from the disintegrating central stalk. May grow up to a few inches per day and is a good water quality indicator.

Udotea spinulosa - This single, broad, fan-shaped bright green leaf on a stiff calcified single stalk is a slow growing species. There are various species in this genus with height ranging from 6 - 8 inches (15 - 20 cm). Prefers a sandy bottom and partially shady areas. Seems to have the same water quality requirements as Halimeda opuntia and besides being a nice looking alga, it's a good water quality indicator.

Neomeris annulata - Another interesting calcareous turf alga that infrequently shows up, sometimes on live rock that has already been in the aquarium for months or years. It forms single short, about 1 - 2 inches bright green stalks. Its called 'Fuzzy Tip or Spindleweed' alga and does not spread and get out of control. Requires strong lighting and moderate water movement to keep it healthy.

Codium spp. - This infrequently seen and a slow growing green calcareous turf algae is usually referred to as 'Dead Man's Fingers,' e.g, Codium intertextum. It mostly forms thick and study finger-like filaments that are somewhat buoyant, yet nice looking and havens for small crustaceans. However, some species can reach a foot in height (30 cm) and most species can easily be dislodged, breaking into smaller pieces and disintegrating. But if controlled, makes for a nice looking and somewhat useful alga.


Generally an encrusting calcareous alga, appearing in a variety of colors, e.g., pink, green, purple, white, yellow, maroon and brown. Most require turbulent water movement, low to medium light intensity of a broad spectrum, calcium level near 400 ppm, maximum magnesium levels (related to salinity level), alkalinity above 3 meq/l and small additions of iodine as iodide. The following are only a few that can show up in the aquarium:

Hydrolithon boergesenii - Encrusting; purple to lavender; spreading in knobby layers. Prefers turbulent water movement and intense light. A favorite surface area for the initial growth of hair algae/bubble algae.

Peyssonnelia sp. - Encrusting; dark red to maroon; edges look like old peeling paint. Prefers shaded areas.

Mesophyllum mesomorphum - Encrusting; over lapping or shelf-like; dark red to pink; very brittle. Found in the Caribbean and Indo-Pacific Ocean.

Sporolithon episporum - Encrusting; reddish brown; spreading in layers that overlap each other. When broken or chipped, exposed surface is white. Prefers turbulent water movement and strong light. This is one of the more common coralline algae. Also a favorite surface for initial growth of hair algae/bubble algae.

Titanoderma prototypum - Encrusting; circular patterns of pinkish cream to red colored small hemispherical bumps that spread and join each other. Requires medium lighting.

Titanoderma bermudense - Encrusting; grayish to pale red; often in overlapping layers. Often with grayish lines on the surface that are the result of the sloughing away of surface cells to keep other organisms from attaching. Requires intense lighting.

Red Algae

The Division Rhodophyta is the largest group of tropical reef algae/plants consisting of over 5000 species. Some of these species contribute to reef building, some serve as a food source, a few can add beauty to the aquarium, and some are troublesome. Whether they can be considered beneficial or unwanted depends upon the species and how its cared for.

As for those in the genera Gracilaria and Halymenia, they are among the prettiest of all red algae, as are the beautiful species Fauchea lacinita, and Scinaia companata. Also showing up in the trade sometimes is Botryocladia uvaria, a red bubble or grape algae that is quite stunning. Most show up attached to live rock and can serve as decoration, a valuable foodstuff for herbivores or a way to export nutrients.

I've found most preferable species of red algae to be quite sensitive to slight changes in water chemistry. Just what those elements or compounds may be, I am not sure but have seen perfectly good specimens quickly disintegrate overnight, even when there were no apparent changes to water quality. Therefore, trace element additions are advised if the goal is keeping any of these species.


Over the tens of thousands of years that invertebrates have lived in the ocean depths, some have developed a symbiotic relationship with alga called 'zooxanthellae.' These brownish-colored (the best color for absorbing blue light) single cell alga utilize the host's nitrogen-laden waste products and carbon dioxide from the surrounding seawater to fuel their energy needs. Their waste products, i.e., sugars and amino acids, leak into the host's body where they are used as a food supply.

Ahermatypic corals lack symbiotic algae and are not considered reef-building corals, whereas Hermatypic corals contain symbiotic algae and are generally classified as reef-building corals. Because of this symbiotic relationship it is important to provide the correct spectrum and intensity of light so efficient photosynthesis will occur. Since blue light is mainly required by zooxanthellae to trigger photosynthesis, lighting equipment should be designed so this portion of the spectrum is given high priority. More on this subject in Chapters 16 and 17.

Unwanted Algae

There is what I consider seven categories of problematic algae and bacteria slime-like growths that cause aquarists the most problems. They are hair algae (long hair-like or plume-like growths); slime algae; turf algae; bubble algae; brown diatom algae; dinoflagellates; and, a very specific green microalgae.

Hair Algae

There are numerous types and colors of algae that are referred to as hair algae with the two of most interest being Derbesia and Bryopsis. These two green filamentous hair-like growths are considered a major pest. Both are presently being considered cyanobacteria that contain chlorophyll. The first and most difficult of the two to overcome is a true hair-like growth called Derbesia. Its long, soft, and hair-like strands can rapidly cover wide areas. Not only can it become somewhat independent of bulk water nutrients once established, trapped detritus/debris can add further nutrients to the bulk water.

The other hair-like alga is Bryopsis plumosa. Its feather-like and upright growing structure occurs as a single stem-like plant with multiple long plume-like tufts. It also can become somewhat independent of nutrients from the surrounding bulk water once the plant structure becomes recognizable.

Both Derbesia and Bryopsis plumosa have two life cycles, i.e., as a small bubble-like growth and that of an easily recognizable plant-like structure. Derbesia has tiny spore packages called 'sporangia' that form along its hair-like strands. When these packages mature, they burst open and release spores that settle and grow into 'gametophytes,' which look like small green bubbles. When these bubbles mature, they release male or female germ cells that eventually unite and form a 'zygote,' which is the base unit for the growth of a new structure of hair algae. Though some aquarists say algae does not grow on surfaces covered with coralline, that is not true. Quite frequently the early stage bubbles of Derbesia can be found attached to surfaces covered with coralline often in the genera Sporolithon and Hydrolithon.

Other occasionally seen algae falling into this grouping include Boodlea, which forms fine, short light green brittle growths that fragment easily. It's sometimes referred as the 'Crunchy Hair Grass.' A similar looking hair algae is Enteromorpha, which is light green and tends to grow in tufts or clusters, and sometimes are found attached to other plants and organisms. There's also a red hair alga in the genus Polysiphonia that can be quite troublesome.

Slime-like Growths

Dark red or black slime/grease-like growths are cyanobacteria, of which those shown here are the most commonly seen. It is photosynthetic and can rapidly cover wide areas, especially in nutrient rich environments. Most of the time it's considered a nuisance because it can get out of control very quickly. However, some very small patches on the substrate should not be cause for alarm as it is one of the earliest microbial colonizers. Only mat-like growths should be removed.

As with some forms of green hair algae, once it begins to form mat-like growths it is capable of becoming somewhat independent of bulk water nutrients. That's because mat-like growths become a barrier to normal diffusion gradients in rock and sandbeds. That barrier negatively affects the normal microbial processes in the substrate they are covering and nearby areas. This benefits the growth of the alga/cyanobacteria structure because the conditions in the below substrate then supply the growth some of its nutrients. And even those mats seen on aquarium side panels are capable of supplying itself some of the needed nutrients once the growth becomes extensive.

Cyanobacteria may sometimes be confused with brown 'grease-like' algae, which is sometimes stringy with bubbles of gas trapped inside. These slime-like growths are usually a very bad case of a diatom or dinoflagellate alga. Both can cover substrate and living animals rapidly.

Another slime-like alga in the plant Kingdom Monera is Phormidium corallyticum. It has been identified as the cause of stony coral and gorgonian Black-band disease. Once this alga's toxic metabolites get near coral tissue, the tissue begins dying. Dead tissue then becomes a food supply for this and other opportunistic bacteria. Further necrosis spreads and as more tissue is affected, it often leads to the loss of the specimen.

Turf Algae

Turf algae is a somewhat broad category consisting of many different forms, e.g., finely branched delicate structures; short and stubby tubular forms; thick grass-like mats; and, both low and/or tall growing forms consisting of leafy lettuce or cabbage-like structures. Depending upon the species, most are not looked upon as desirable, however, some do have useful purposes such as nutrient export and in small 'controlled' amounts may look quite pleasant.

Some of the more interesting green species have thicker branched growth than what is generally referred to as hair algae, and they include the Cladophora species, e.g., Cladophora prolifera, Chlorodesmis fastigiata (Turle Weed), and possibly those in the Cladophoropsis genus. These have tubular filaments and grow similar to clumps of grass. Since the species within these genera are not palatable to most herbivorous fishes, it generally spreads, especially in older nutrient rich aquariums.

There's also Ulva, and species in this genus are usually referred to as 'Sea Lettuce.' They have soft sheet-like leaves that can grow rapidly in nutrient rich environments, and also just as quickly disintegrate. It's a tasty food for herbivores, but best suited for refugia or slow flowing alga turf filters.

One rarely seen and difficult species to manage for any length of time is Acetabularia crennulata, sometimes called Mermaids Cup. Nice looking yet requires extremely good lighting, as it's a very shallow water species. Usually dissipates quite rapidly in most aquaria.

The species in the genus Dictyota, e.g., Dictyota bartayresii, are brown, somewhat flat Y-shaped branched algae that often arrives on live rock. In fact, there are even yellow-brown, green-hued, and purple varieties, with one even having an iridescent blue color. It can grow quickly and fragments easily, spreading throughout the aquarium. It shades out corals and will attach itself to their skeleton causing the recession of living tissue. Unfortunately it does well in average aquarium seawater conditions and is not palatable to most herbivorous fishes.

Another brown alga usually arriving on live rock is Lobophora variegata or what is referred to as 'Brown Wafer Algae.' Sometimes its confused with various Padina spp., e.g., Padina australis, which form similar low scroll-like shapes. Both are temporary growths as they come from areas high in nutrients and are not tasty foodstuff for most herbivorous fishes. Its best to remove them before they decay in the aquarium.

As for some of the more difficult red turf algae, Nitophyllum punctatum is a somewhat flat Y-shaped branched alga that often arrives on live rock and looks quite similar to brown Dictyota. But it ends there as this species is delicate and is readily eaten by herbivorous fishes. And in fact, it's so delicate and sensitive to small changes in water quality that an excellent growth can disintegrate in one day. Another is Galaxaura, which forms small bushes with stiff wiry branches. It's not palatable and is a detritus collector, however, may look nice if controlled in small amounts but does not serve any other useful purpose.

Gelidium is another reddish or purplish turf alga, e.g., G. pusillum that arrives sometimes on live rock taken from shallow intertidal areas where there is wave action. Its somewhat short 2 inch (5 cm) thin fronds are firmly attached to the substrate. It's a wiry type turf algae that needs extremely bright light, very good water movement, and a somewhat nutrient rich environment. In most cases its best removed before the substrate or rock enters the aquarium as once in the aquarium it seems to spread and become troublesome, as its difficult to remove and begins to crowd out corals..

Wrangelia argus is another purple-red short soft turf alga forming fuzzy clumps on substrate. It can arrive on live rock that was subjected to very high nutrient areas in shallow turbulent areas. It can spread to other rock and/or sandy surfaces in the aquarium. Rock with any signs of this pest need to first be scrubbed clean before entering the aquarium. If it develops in the aquarium, it should be siphoned out and water quality improved.

Whether Hypnea musciformis, a dark purple mat-like red alga consisting of tangled branches with pointed tips is a pest depends upon who has experience with it. It grows in an interwoven fashion and can be found between the branches of corals or simply covering wide areas. Sometimes called 'Hookweed' this alga can shade out corals and become problematic.

An immensely troublesome red species, and the worst I've ever come across is one that took almost two years of weekly efforts to stop its growths from appearing on interior equipment, live coral skeleton surfaces, sandbed surfaces and live rock in one of my past aquariums. It's widely called Red Bubble or Red Valonia Alga, and is technically called Botryocladia skottsbergii. In the wild, its widely distributed: Indian Ocean, Western, Central and Eastern Pacific, and the Mediterranean, with it arriving mostly in the aquarium trade from the Philippines on live rock and various coral specimens. It is also found in Hawaii, Maldives, America Samoa, Marshall Islands, and California waters. Unfortunately, it survives exceptionally well in nutrient poor waters!

And even though there are some nice species in this genus, as mentioned above, this is not one of them! This species forms interconnected low growing bladders, which are filled with a syrup-like fluid. Growths, beginning with small red wine-colored bubbles 2 – 10 mm in height then spread a base that erupts with new short-stemmed bubbles/bladders, with older bubbles often reaching heights of .5 inch (1 cm) or more. As the base spreads it encrusts living organisms, crowding them out and opening new substrate areas for its growth. When bubbles become large and spotted, they are ready to burst open!

When bubbles open its liquid slowly flows into the surrounding water no doubt spreading new spores to other areas in the aquarium. In fact, once the bladder surface forms small spots it is said to be ready for sexual reproduction, which seems from my sad experience to occur within a couple of months of it forming new bladders. Nothing in the aquarium will escape these growths.

Unfortunately, the spread of new growths seem to occur in systems with near zero phosphates and nitrates, therefore its spread cannot be eliminated by maintaining high quality water parameters. Furthermore, have not seen any of the well-known algae consumers such as various species urchins, crabs, sea hares, and well known herbivorous fish even nibble on this alga! And it even grows in shady areas! I have a suspicion that iodine additions may accelerate its growth and/or the alga itself naturally contains a high level of iodine resulting in a bad taste to grazers, but at this time it's only a theory.

Since there are no known predators of this invasive species, and I've tried several to no avail, under no circumstances should it be allowed to continue 'anywhere' the aquarium! Regrettably, this means when first seen, 'whatever' its on must be removed from the aquarium if at all possible and wiped clean with the area of removal flushed clean before its return to the aquarium. And it's far better to do this when 'first' seen, as this species tends to spread quite quickly as I've sadly witnessed!

From time-to-time I've also seen red filamentous Centroceras clavulatum attached to newly received live rock. Rarely does it do well for any appreciable length of time and its best to remove it before the rock enters the aquarium.

As with some of the above-mentioned algae, small amounts present no problems in most aquariums. In some ways they can serve as a food supply for some herbivorous animals, a way to export some nutrients, or at least a conversation item. However, most become a problem if not diligently controlled. And when these type turf algae become well established, it may become an overwhelming situation to rectify. Better for you to be in control than them!

Bubble Algae

Various types of green bubble algae have certainly become a problem for some aquarists over the past decade. In fact, some of their bubbles can grow fairly large and have seen them as large as 2 inches (5 cm). Unfortunately when their membrane-like wall material wears out or ruptures, internally forming new cells/bubbles are released and can rapidly spread throughout the system. It's always more wise to remove the object they are growing on and scrape it off outside the aquarium if at all possible. Otherwise, with great care while in the aquarium, try to remove without breaking them!

Those in the genera Valonia, Ventricaria and Dictyosphaeria cavernosa have bubble-like growth that can be oval, spherical, or tube-shaped. Mostly, they attach themselves in rock crevices or depressions where nutrients tend to collect. They grow well under various lighting intensities and even do exceptionally well in aquariums with very low bulk water nutrients.

Brown Diatom Algae

Probably the most common brown algae are the brown diatoms. They are usually one of the aquarium's most common and often first colonizers. These algae can be sheet or film-like in appearance, appear as tiny brown dots on the aquarium inside panels, or cover the substrate surface where there is sufficient light. Silica/silicate is used in the structure of their cell walls. Depending upon the amount of silicate in solution, their growth can present anything from minor to major labor-intensive cleaning tasks. Besides appearance, when heavily coating objects it can photosynthesize and produce oxygen bubbles, which in severe cases may raise pH to dangerously high levels (above 8.5).


Another type of problematic slime-like brown alga is caused by a dinoflagellate. It can result in large areas, including the surfaces of invertebrates, being coated in a brown gelatinous mass. It is usually introduced on a new piece of live rock or coral animal and can easily become problematic if the bulk water is rich in organic material.

This free-swimming alga is extremely difficult to cure. Silicate is not one of its needs as is the case with diatoms. Unfortunately calcium carbonate is. Since we cannot rid the aquarium of its calcium carbonate content, the various methods described in 'Remedies' below should be employed. Keep in mind a small microscope would help identify which form of brown algae is in the aquarium. If the alga cell has a flagellum, i.e., a tail (for propelling itself through water), it is a dinoflagellate.

Green Microalgae

There is a particular parasitic form of green microalgae that can occur in the calcium carbonate skeleton of stony corals. This boring microalgae, Ostreobium, grows inside coral skeleton material. It reduces the structural strength of the skeleton material and interferes with the animal depositing new skeleton material. Any stony coral that may exhibit a greenish coloration in its skeleton should not be purchased, as curing the problem area is not feasible.

Contributing Factors

There are a number of factors that lend themselves to the beginning or continuance of nuisance algae and/or slime-like growths. Some of these are what could be considered 'indirect' causes, such as overcrowding and overfeeding. These of course lead to poor water quality, which now contains the direct causes, such as excessive nitrogen-laden compounds, phosphate, silica/silicon, and incorrect use of certain additives such as iron and molybdenum. The nitrogen-laden compounds, such as ammonium, nitrite, and nitrate, were already discussed in Chapter 10. And even though there was some discussion on silica/silicone, iron, and molybdenum in Chapter 9, those and phosphate need further discussion.

Maintaining Low Phosphate Levels

Most aquarists realize that once system nutrients become excessive, growths of unwanted forms of algae are a very real possibility, if not already occurring. Unfortunately, some aquarists fail to realize why and where these nutrients come from, thereby failing to limit their introduction or accumulation in their closed systems. And 'closed systems' are extremely important words here, as the confines of our aquaria help present a more bay-like environment than the hoped for fringing reef-like environment that attracts many to this hobby. And since phosphate is one of the more important nutrients, it is vital to understand where this compound comes from and how to limit its accumulation in closed systems.

Phosphate is a compound, which consists of phosphorus (P) and oxygen (O). During microbial processes, they combine forming a compound called phosphate. It consists of one atom of phosphorus and four atoms of oxygen (PO4). As for phosphorus, it is an important; in fact a necessary building block in all life as it is part of every DNA molecule. It enters the ocean from land and undersea volcanoes as Dissolved Inorganic Phosphorus (DIP). There are two other forms of phosphorus: Dissolved Organic Phosphorus (DOP) from ruptured algae cells, animals, and bacteria, and Particulate Organic Phosphorus (POP) as part of detritus and other organic matter.

Phosphate/orthophosphate (DIP) is the most important of the three and a major nutrient for alga growth and which can also interfere with the growth of some of our prized corals. Yet, is still needed in minute quantities by animals, including symbiotic and coralline algae. It's also thought to cause graying hair in some aquarists!

If closed systems had the exact same processes as the oceans, phosphate would almost always be below detectable limits using the 'average' aquarium test kit. Some of these kits have a low reading of 0.05 ppm and the ocean has a concentration of approximately 0.03 ppm. Therefore highly recommend looking for a much higher quality test kit for this important seawater parameter!

There are several ways in which phosphate enters the closed system. Tap water is one of those ways since phosphate is used as a fertilizer on many farms. It tends to percolate downward and enter the aquifer or washes off the ground surfaces and enters nearby rivers and streams. It then finds it way into local water impoundments and eventually flows from private or municipal water suppliers to the tap. Some local water companies also use phosphate as an additive to control rust in metal pipes and fittings. Getting an analysis of the incoming water to your place of business or home, or sampling it yourself is a good first step to take before using it in the aquarium.

Phosphate may also enter the aquarium when activated carbon is used, including those that are acid washed. It's also possible for certain substrates used in calcium reactors to introduce phosphate. The low pH in these reactors make it easy to dissolve calcareous material that may have it in their makeup or at one time became coated with a precipitant containing phosphate. It is wise to only use a quality calcareous material, one not containing shell material or old coral skeleton material. Keep in mind that shell-type animals consume algae and/or filter feed on organisms containing algae and heavy metals. It is then incorporated into their shell only to be leached back into solution by the calcium reactor's low pH. And old dead coral skeleton material may have also become coated with phosphate at one time!

Nevertheless, the majority of phosphate seen in aquaria is from the types of foods being fed to its inhabitants, whether that's from excesses not eaten or the animals' waste products. Both are reduced/oxidized by bacteria, with phosphate one of the end results.

Actually, most aquarists paid very little attention to phosphate levels until reef aquariums became popular in the mid 80's. It then became fashionable to keep heavy growths of macroalgae so as to help limit the accumulation of nutrients. In fact, there still isn't anything wrong with that depending upon the type of ecosystem that is being maintained. But hair algae and other types of unwanted algae are another story, especially in more complex reef systems.

Since there is no way or any reason to completely eliminate phosphate, the question becomes just how much is too much. In the reef aquarium environment there is no doubt it should be kept below .05 ppm, with <.02 ppm a more preferable target. In fish-only systems, anything above .1 ppm should be a signal to review husbandry practices.

For those that use Kalkwasser as a means to supplement calcium ions, it also can serve as a way to precipitate some phosphate. The precipitant, calcium phosphate, will not normally reenter solution or be utilized by algae or bacteria unless subjected to a very low pH or an area where bacteria attack it for its oxygen content, such as under slime-like growths. The probability for these events occurring is slim, yet not impossible; therefore I prefer keeping phosphate as low as possible and more products are coming to market to make that effort quite easy as already discussed in Chapter 4 & 6.

Keep in mind aquarium test kits check only for inorganic phosphate/orthophosphate. Organic phosphate, i.e., phosphate tied to detritus and other organic substances do not register on phosphate test kits utilized by hobbyists, nor is it removed by phosphate removing media. Therefore it's possible to have greater amounts of phosphate than what registers on these type test kits.

Because of that recommend the use of phosphate removing media as soon as the aquarium is up and running and if at all possible, replacing the media as soon as any level result can be seen on a test kit sample. And testing should occur weekly until the system is well established. Then monthly should suffice unless some major bio-load changes are made. Keep in mind severe modifications to system biological filtration/live rock/sandbed can cause upsurges in the organic phosphate level, possibly quickly leading to a cyanobacteria problem.

There are numerous ways to limit the amount of phosphate that 'enters' the aquarium. For instance:

  • Testing tap water supply and if necessary using RO, DI, or distilled water for water changes and evaporation make-up.

  • The use of a quality protein skimmer to remove unwanted compounds prior to them breaking down and adding to the pollution problem. Keep in mind skimmer airborne particles tend to accumulate on the inside of the top cover of the waste collection cup. These particles contain orthophosphate. Frequent cleaning, daily if possible, of this area alone will enhance phosphate reduction.

  • The reduction of detritus buildup by keeping mechanical filter media clean and/or vacuuming substrate as needed.

  • Not overcrowding and/or overfeeding.

  • Soak and aerate all activated carbon in RO, DI, or distilled water prior to use. Then test and if okay that's a brand to stay with.

  • Siphoning out the upper most sand particles in living sand systems every three or four months. This exports sand particles possibly coated with calcium phosphate in this active area.

  • Check the label of aquarium additives to see if they contain phosphate. If it does not say 'No Phosphates' check with their manufacturer.

  • Make sure only a quality salt mix is used. Don't be fooled by fancy claims. Contact other aquarists or aquarium societies for their comments and recommendations.

Do not wait until the green monster raises its ugly head to test and begin controlling phosphate. Once unwanted forms of algae begin, they become labor intensive and expensive to resolve, and sometimes no longer feasible to resolve! Gray hair and empty wallets are then forthcoming.


As explained in Chapter 9, the element Silicon takes on many forms, nevertheless, its silicic acid form is the general cause of brown diatoms.

Evaporation make-up water, even if processed through a reverse osmoses system, will still contain this nutrient. In fact, there are no reverse osmoses units that will remove 100% of this element, and even quality units remove only about 90%. To remove all silicate from tap water a proper combination of resins in a well-engineered deionization unit must be used with the water first flowing through an RO unit. This is necessary in order to remover the majority of its ions so they don't prematurely clog the resins in the DI unit. Salt mixes should also be tested prior to use no matter what is on their labels or in their advertisements.

And as previously mentioned, anything that may be composed of silica has a slight solvency at the pH marine aquariums are maintained. In fact, silica begins to go into solution at a pH of 8.0. It greatly accelerates its solvency at a pH of 8.5. The result can increase the proliferation of nuisance brown algae and increase the amount of time it takes to maintain a system, whether that's a fish-only or reef system.

Should aquarium water be tested for silica? In my opinion, no - as its actually more prudent to test the water used for evaporation makeup or water changes. Keep in mind if the water going into the aquarium has any silica/silicate, the result will be some diatom growth of one degree or another. The use of silica in diatom formation occurs quite rapidly, therefore aquarium water itself may not show any significant level of silica even though diatoms have or are forming. Yet, testing the aquarium water if severe diatom-like growth exists is useful if for no other reason than to determine whether the growth is a brown diatom or possibly that of brown dinoflagellate algae. Some phosphate removing medias also remove silica.

Iron (Fe)

Iron is a minor trace element found in NSW and is necessary for algae biological oxidation/reduction and chlorophyll production along with animal/coral coloration and growth. Without it, photosynthesis would not occur, and as for those corals with zooxanthellae, they would perish. How much is required for these various functions remains difficult to quantify, yet some recommendations have surfaced saying that 0.1ppm be maintained in all aquariums. This was no doubt from someone selling Iron additives, as it makes no sense for 'all' aquariums to have such a high iron content since its level in NSW ranges from 0.002 – 0.02ppm. Nevertheless, if the goal were to have copious amounts of healthy macroalgae, then occasional doses between 0.025 - 0.1ppm might be helpful in maintaining its growth. In fact, one of my old reef systems in the later 70's contained a heavy growth of macroalgae and seemed to benefit from every other week experimental doses of a non-chelated Iron 'houseplant' solution.

And 'briefly' elevated was the correct term in those days, as Iron exists in two forms in seawater, i.e., Iron with two positive charges (the bioavailable form), and Iron that has lost an electron to another molecule, therefore gaining a third positive charge, e.g., rust. In fact, most Iron in seawater is the latter, as Iron with two positive charges is quickly oxidized into this ionic form. Therefore, unless an Iron additive is chelated, it will quickly precipitate out of solution at a pH of 8.0 and above. As for Iron additives these days, they are usually chelated with EDTA or citrate, and gradually release bioavailable Iron over the forthcoming days. How often it needs to be applied, depends upon system goals. Nevertheless, for systems that do not employ large amounts of macroalgae, water changes will adequately replenish their Iron needs.

Beware, as the over usage of these type products may cause unwanted cyanobacteria blooms, especially in low-lit areas. And if used in more complex reef systems, over usage may foster release of phosphate bound to calcareous material in areas subjected to the sulfur cycle. And since the sulfur cycle is a normal microbial process in all sandbeds, only very minor additions, possibly for enhancing coral colors, is recommended unless the goal is to foster algae growth. Forewarned is forearmed as excessive use of Iron additives can contribute greatly to encouraging unwanted forms of algae.

Testing for Iron in most aquaria is not required unless there is a desire for lush growths of macroalgae, however, testing the tap water used for evaporation makeup or water changes is another matter. In fact, in some areas where the groundwater source is near high deposits of iron ore, it can easily find its way into the drinking water. Having a good handle on the freshwater source when it comes to plant nutrients such as nitrate, phosphate, silica, and iron makes good sense!

Molybdenum (Mo)

This trace element is essential to nitrogen-fixing organisms, e.g., cyanobacteria (red slime algae) and possibly zooxanthellae to some degree.

Yet where reef aquariums are concerned, it's a nonessential additive in my opinion unless copious amounts of algae are desired. It's normally found in NSW at 0.01 ppm, and can be supplied via the salt mix used for normal water changes.

Molybdenum, pronounced 'ma-lib-de-num,' in conjunction with phosphate including DOP and POP along with sufficient light, is a major algae enhancer. Depending upon system goal, this is an additive that may or may not be needed, in fact is only best used where lush growths of algae are desired.

Water Movement

One of the most overlooked parameters in both fish-only and reef aquariums is good movement of the medium itself. Most aquarists realize water movement is a way of bringing oxygen to the animals in the aquarium and reducing the influence of carbon dioxide on the carbonate buffering system. Insufficient water movement can also lead to detritus accumulations. It then breaks down adding nutrients to the surrounding water or settles in crevices where algae of one kind or another can get a foothold. Increasing water flow with surge devices or large powerheads not only helps to eliminate low flow areas that favor cyanobacteria, but also helps suspend detritus long enough for mechanical filtration to remove some of it.

Light Refraction

Some aquarists blame the quality of their lights for algae growth, and others blame copious amounts of dissolved nutrients. There's even the thought new lamps, which have greater intensity than older lamps, may enhance alga growth. However, none of these by themselves are totally true. Light alone cannot cause the growth of algae. Nutrients alone cannot cause the growth of algae. But combine them and there will be algae growth, both good and bad.

Keep in mind if the aquariums bulk water contains copious amounts of skewed constituents, whether from an excessive bioload or additive products, even the addition of new lamps having a quality spectrum and intensity will enhance algae growth! The reason for this is that skewed bulk water element levels are taking the blue-green spectrum waveband coming from the lamp and changing it into a more red band wave length that algae prefer. The point here is that light alone cannot be blamed for unwanted algae growth. However, a quality light spectrum, i.e., in the blue-green band wave, can shunt the growth of algae 'if' the water it is passing through is more like that of NSW.

Live Rock Selection & Placement

One of the most overlooked causes of initial algae problems in some new aquariums is with the use of poorly collected, processed and transported live rock. Because of these poor practices, organisms that originally lived on or inside the rock when first collected became subjected to air and perish in a short time thereafter. The resultant nutrients from their die-off on both internal and external surfaces, if not properly cared for before entering the aquarium, are simply more than a newly established system can adequately process. Therefore, curing live rock before use along with duplicating nature, not a brick wall or a pyramid-shaped structure where detritus would collect under, is a more correct approach. Also, the quantity of rock used is another factor, as too much restricts water flow and also provides a lot of anaerobic area where inefficient denitrification occurs. All of the above can contribute to diminishing water quality, thereby helping to initiate and sustained growths of unwanted algae. Go back to Chapter 6 and reread and heed the thoughts on Live Rock.

Filtration Choices

Some new aquarists consider filtration as a process that renders crystal clear water. Actually, 'filtration' should be considered a process that renders 'quality' water. And the only way to attain quality water is by becoming familiar with the different forms of filtration before the system is established. Keep in mind that biological, chemical, and mechanical filtration each add their own unique contribution to the overall health of a closed system. If properly established and maintained, they act together as a team and help to provide a balanced environment when commonsense is used to control system bioload.

Overcrowding & Overfeeding

Even though lack of microbial equilibrium and balanced filtration processes are the direct causes of unwanted algae, overfeeding and/or overcrowding should be considered the indirect contributing causes. Algae require nutrients, e.g., nitrogen-laden compounds, and light to get started. In crowded or overfed closed systems the nutrients required for algae growth can easily be attained. In fact, not only easily attained, but they also tune the spectrum (light) to something better suiting the needs of algae!

As mentioned in Chapter 10 and worthwhile repeating here, there's some aquarists that think their fish need three square meals per day. Would agree some fishes such as angelfishes and tangs fare better with numerous small feedings per day. Nevertheless, in the wild, fishes need to work very hard at getting their required nutrients. They may go long periods without finding proper nourishment. When food is available, their metabolism is excellent and their waste products are usually void of unprocessed food. Yet in the aquarium, they are certainly not getting the same level of exercise as in the wild. Over abundance of food from the over-generous aquarist can certainly lead to poorly metabolized waste products, and this contributes to poor water quality. It's better to understand the nutritional needs of the animals, then meet those needs, but not exceed them. Without a doubt, overfeeding only hastens diminishing water quality, and often initiates slime-like growths and supports the increases of unwanted algae growths.


In the wild, herbivores concentrate their efforts in areas where alga growth is plentiful. In some areas of the Sea of Cortez I've seen urchins by the thousands come out in the early evening and begin scouring the rocks in the shallows. Much of their waste products are quickly broken down by turbulent water movement and dispersed into the surrounding water. And even though their wastes probably have little impact on the surrounding water because of local water currents, continued algae growth in the area reoccurs because of sewage discharge from nearby hotels.

Yet in the aquarium, waste products from large amounts of herbivores, both fish and invertebrates, unless siphoned out add further nutrients to the overall system. Therefore an aquarium already skewed in favor of algae growth would very possibly only see temporary results if a large amount of herbivores were added. Yet there's no doubt reasonable use of herbivores is helpful in many closed systems. But in systems with prolific unwanted algae growths it makes more sense in my opinion to limit nutrient sources, besides physically reducing overly abundant growths.

And if herbivores are required, it is wiser to first remove any readily accessible algae growths by hand before allowing them access, as the less they have to turn into fecal pellets the better off the entire system will be. As for some herbivorous fishes, once they become accustomed to a free meal, i.e., being hand fed different foods, they sometimes seem less willing to vigorously devour algae in the aquarium.

Biological Control

Natural reduction of algae, whether the good, bad or ugly, is sometimes referred to as 'biological control' and has great value if handled correctly in the closed system.

Since there are biological control species that consume only certain forms of algae, I've created six, broad-ranging algae categories. Its number will appear in front of the herbivores listed further below indicating what general category they would be most useful for. A much wider species-specific list of both algae and control species can be found on this website along with their photos.

1- Filamentous

2- Macroalgae/Micro/Turf algae

3- Coralline

4- Cyanobacteria

5- Diatoms

6- Bubble Algae

1 - Surgeonfishes - the genus Zebrasoma, e.g., Zebrasoma flavescens

2, 4 & 5 - Surgeonfishes - the genus Ctenochaetus, e.g., Ctenochaetus hawaiiensis

1 & 2 - Surgeonfishes - the genus Acanthurus, e.g., Acanthurus leucosternon

1, 2 & 6 - Surgeonfishes - the genus Naso, e.g., Naso lituratus

1 & 4 - Blenny - Ecsenius bicolor - (first trim algae to a short height)

1, 2 & 4 - Blenny - Ophioblennius atlanticus - Atlantic Red-lip Blenny

2 - Blenny - Salarias fasciatus – Lawnmower Blenny – Mostly microalgae

1, 2 & 6 - Rabbitfish – the genus Siganus, e.g., Siganus guttatus

1 & 2 - Angelfish – the genus Centropyge, e.g., Centropyge argi – and many other species - acanthops, aurantia, bispinosus, eibli, fisheri, flavissima, heraldi, loricula, nox, resplendens, shepardi, vroliki - however most nip invertebrates

1 - Gobies – the genus Amblygobius – e.g., Amblygobius hectori, and Amblygobius rainfordi

1 & 6 - Emerald Crab - Mithrax sculptus - can get big enough to be a danger to small fish

1 & 4 - Blue-legged Hermit Crab - Clibanarius tricolor - first trim hair algae to a short height

2 - Red-legged Hermit Crab - Calcinus tibicen

2 & 3 - Blue-spotted Hermit Crab - Clibanarius digueti - seems to prefer coralline to green algae

2 & 3 - Polka-dotted Hermit Crab - Phimochirus operculatus

1 & 2 - Scarlet-legged Hermit Crab - Paguristes cadenati

2 & 3 - Sally Lightfoot Crab - Percnon gibbesi

1 & 2 - Conch - Strombus alatus, Strombus gigas - very good green alga eaters. Captive bred and very hardy

1 - Sea Slug -Tridachia crispata - Florida Lettuce Slug is very fond of Bryopsis. Also the slugs Elysia ornata and Elysia diomedea

1, 2, 3 & 6 - Urchins - Black Longspine Diadema setosum is one of the better choices, so is the Tuxedo Urchin Mespilia globulus. However they bulldoze corals and strip coralline

1, 2 & 5 - Snails - Astraea tectum snails appear to be much better suited for longevity in closed systems than the Turbo fluctuosus species or those in the Nerita genus. Quantity needed would be in the range of one per ten gallons in well-maintained systems

4 & 5 - Snails – Cerith's such as Cerithium echinatum, Cerithium muscarium

1 - Snail -Trochus niloticus - Very hardy

Also take note that large populations of copepods and amphipods can control some forms of minor green algae growths. These crustaceans proliferate if the system is somewhat devoid of carnivorous animals that find them a tasty meal.

Check List

There are numerous reasons why unwanted forms of algae and cyanobacteria show up in the aquarium. I'll first attempt to briefly list all possible causes, some of which may not be applicable in some circumstances. The point here is to surface as many possibilities in as concise a manner as possible. Then let you, the reader pick those that may apply and then look through 'Remedies' to find what may help resolved the problem. Some of the 'Causes' noted below may seem extremely simple because they are; however, awareness of these causes goes a long way in preventing them in the first place.


  • Less than adequate biological and chemical filtration methods used to set-up the aquarium.

  • Overfeeding, especially with products like flake or frozen foods, can easily lead to 'pockets' of uneaten food or partially metabolized waste products. These pocket areas are perfect breeding areas for cyanobacteria. Once started, sheet-like cyanobacteria can quickly spread, even in dimly lit areas.

  • Brown diatoms are caused by silicate usually introduced into the aquarium via make-up water, the salt mix itself, silica sand, or something in the aquarium that may be composed of a silica substance.

  • Dinoflagellates, free-swimming brown algae, can be introduced with live rock or coral. Under the right circumstances, i.e., water rich in organic material, they can multiply rapidly and form stringy globs of bubble filled goo. They can produce toxic side chemicals that further reduce water quality, making it more to their liking and other forms of unwanted algae.

  • Overcrowding - the more fish the more food needs to be fed. This results in more waste products, simply leading to more nutrients in the bulk water.

  • It is quite normal for a new system to develop some forms of algae while the system is developing its initial microbial processes. Some may dissipate quite quickly, however others may gain a foothold. If the system has more nitrogen-laden compound producing processes than efficient denitrification processes, it contributes to on-going conditions favoring alga growth.

  • The use of Diatomaceous Earth (DE), i.e., the skeletons of tiny single cell diatoms composed of silica, for filtering purposes can lead to brown diatom alga problems.

  • The use of unprocessed tap water, if containing plant nutrients, can lead to unwanted forms of algae.

  • Medications can greatly reduce the efficiency of biological filtration. They destroy or inhibit bacteria and part of the result can be a rise in ammonia level. If experiencing any levels of ammonia, the safest thing to do is not add any further bio-load to the system until the source of the ammonia is resolved.

  • The over use of certain additives can lead to unwanted algae growths. Not only do some additives directly influence algae growth, they may also indirectly affect them by increasing the level of seawater constituents above NSW levels, thereby negatively influencing the spectrum of the delivered light.

  • Some salt mix formulas may contain algae nutrients.

  • Lamps may be too old or incorrect spectrum.

  • Failure to properly use protein skimming or activated carbon.

  • Poor water movement.

  • Crashing macroalgae growths quickly add to the nutrient level. The decomposition of dead algae adds nutrients and vitamins to the bulk water.

  • Carnivorous fishes may be eating too much of the microfauna, i.e., copepods and amphipods, that naturally feed upon microalgae.

  • Sand sifters/snails are dying in hidden areas and not being removed, thereby adding to the nutrient level.

  • Lack of water changes.

  • Die-off of some organisms living on or in newly installed live rock can result in an excessive initial nutrient level which in turn leads to giving algae a chance to gain a foothold.

  • Starting systems with dead rock, e.g., dry tuffa/lava/concrete rock, and dry, dead sand. Dead rock has no beneficial bacteria living either in or on it. That may allow unwanted nutrient levels in the aquarium to rise without being processed by beneficial bacteria that would have normally inhabited live rock/sand.

  • Not keeping the mechanical filter clean.

  • Using Molybdenum, which is an alga-enhancing trace element.

  • Brown and red algae growth can be enhanced by the over usage of potassium iodide.

  • Undergravel filter substrate, if so equipped, may be too deep or water flow through it too slow. Gravel then becomes a dirt trap, which adds greatly to bulk water nutrient content.

  • Not keeping a reasonably clean aquarium will add unwanted nutrients. Detritus breaks down into phosphate and nitrates very quickly.

  • The green algae Ostreobium, sometimes found in coral skeletons, is nourished by excessive nitrate and phosphate levels.

  • Cyanobacteria is caused by the accumulation of nutrients caused by overfeeding/overcrowding, poor water movement, poorly balanced filtration, and lamps high in the red spectrum.

  • Over usage of additives containing iron.

  • Slacking off on regular maintenance.

  • Using a poor grade of calcareous material in a calcium reactor, such as a mix high in shell debris, which normally contains high amounts of phosphate and heavy metals.

  • Having too many areas in the aquarium where no maintenance can be performed, such as excessive amounts of improperly place rock.

  • Failing to use the right types or combination of herbivores.


Unwanted forms of algae are clearly a widespread problem. Herbivores, a more natural approach to algae control were discussed above and their use will not be repeated here, nevertheless, if using herbivorous animals, use commonsense stocking levels.

Over the past few decades I've heard of many remedies that have worked well for aquarists. Some may be extremely helpful in one situation and not so in others. To be more concise, I've divided this section into subsections beginning with those remedies that are wide ranging and encompass hair algae and turf algae problems. Then note those that are more applicable to diatoms, dinoflagellates, and cyanobacteria.

General Controls/Comments

  • Do not add trace elements of any kind until an alga problem is resolved.

  • Check the label of any aquarium additive to see if it contains plant nutrients. If not sure, contact its manufacturer.

  • Adding some macroalgae, e.g., Caulerpa, may help assimilate some of the very nutrients pest algae utilize.

  • Siphon off accumulating detritus.

  • Test tap water before use. If needed, use RO and/or DI filtration prior to use. Preferably both.

  • Vacuum up/remove the upper most sand particles in living sand systems every three or four months. This may export some sand particles coated with calcium phosphate, a result of the mineralization process in the upper sand level.

  • Medications to kill unwanted algae/cyanobacteria may result in only temporary good results, therefore more forethought as to other means of control is highly recommended.

  • If the local water company adds chloramine to your tap water, it should be removed prior to use, as it is a source of ammonia. The chloramine compound, a combination of ammonia and chlorine, is much more difficult to remove than simple chlorine. If unsure whether chloramine is a component of the tap water, call the local water supply company for information.

  • Turf algae are often easily removed with tweezers. In areas where there are clumps, simply grabbing the center area with a big tweezers and applying a slight upward pulling motion usually removes a large clump.

  • Use a turkey baster to blast clean turf algae areas. Keeping them free of detritus reduces nutrient accumulation in the bulk water.

  • The use of a turkey baster or a small powerhead to keep rock crevices clean of detritus will help decrease the possibility of bubble alga growth, as will excellent water movement/surges of water.

  • In UGF systems the correct water flow through the substrate should be approximately 6 to 8 times the volume of the aquarium. Also, having no more than 2 inches of gravel, gently stirring it once a week and vacuuming it every two weeks goes a long way in correctly maintaining a more algae free system when this type filtration is utilized.

  • Keep in mind as hermit crabs grow, they need larger shells. Provide some empty shells in the system.

  • Bryopsis plumosa is sometimes fairly easy to control because it is usually a single stem plant. Simply remove the entire plant structure at its base.

  • Bubble algae cells or bubbles are held to the rock by tiny root-like appendages. A pointed, yet dull knife blade slipped under the cell(s) can pop them loose and the entire cell or group of cells can easily be removed from the aquarium unbroken. Try not to break them as the bubble contains many new little bubbles that can spread the problem.

  • Sandbeds should occasionally be surveyed for slab-like conditions and if necessary, broken up into individual grains. Keep in mind anaerobic areas under these slabs foster the denitrification process called ammonification, which only reduces nitrate to ammonium.

  • Use a quality protein skimmer, as it helps remove unwanted compounds prior to them breaking down. Also, the skimmers airborne particles, which tend to accumulate on the inside of the top cover of the unit, contain orthophosphate. Frequent cleaning of this area is highly recommended. Skimmers also aerate the water thereby removing some carbon dioxide, also a plant nutrient.

  • Use activated carbon that is termed 'phosphate free.' If not sure, soak and aerate a small portion of the activated carbon in either RO/DI or distilled water for a few hours and then test its water.

  • Consider the use of ozone to help reduce nutrients and the transportation of alga cells. And/or an ultraviolet (UV) sterilization device to help reduce the transportation of alga cells.

  • Molybdenum is an alga enhancer. Greatly reduce or discontinue its use. The same is true of iron additives, and possible other trace type additives.

  • Vacuum substrate monthly or more often if needed.

  • There are very specific types of equipment that accomplish the denitrification process, i.e., removal of nitrate directly from aquarium water. Most are small biological systems that use special additives to promote the process. Any type equipment that fosters anaerobic denitrification must be fully understood before using!

  • Replace or wash mechanical filter media every few days.

  • If an unexpected algae bloom quickly occurs, check with the local water supplier to see if an anti-rust inhibitor was added to their distribution system before you consider other ways to resolve it. If so, first process the bulk water through activated carbon and ion exchange molecular absorption filters to help reduce/eliminate those nutrients before taking other possible needed steps.

  • For an out-of-control hair algae problem and where the rock is worth saving, I recommend using the following mechanical method. - Depending on just how severe the problem is, removed any rocks that can be easily removed and brushed them clean in a pail of water the same temperature and salinity as the aquarium. Temporarily store them in a container filled with some freshly prepared seawater. For the more difficult areas, wrap a long, wire handle, fairly stiff pipe/tube brush (something that would fit inside a half-inch ID tube) around a siphon hose. Make sure the brush portion is even with the end of the siphon hose. With the siphon action started, scrub the areas of hair algae. Pinch the end of the hose as needed to prevent too much water being drawn in when not necessary. Where hair algae gets caught on the brush, remove it by hand. Where it is drawn into the siphon tube, allow it to simply flow into the wastewater collection pail. When ready to replace the removed rock, scrub it with some white vinegar, rinse with seawater and place back in the aquarium. The vinegar is used to lessen any calcium phosphate that originally adhered to the rock surface. All water removed should be replaced with freshly prepared seawater. This labor-intensive method is usually quite successful, however, this method may have to be repeated a few times. Each time the hair algae will become less. It is a tough way to beat the problem, but if the rock is worth saving this method works. Keep in mind the source of the excessive phosphate/nitrate needs to be eliminated or the problem will simply continue.

  • Poor grades of salt mixes can initiate unwanted algae. Check not only their phosphate, silicates, and nitrate levels, but also their ammonia level when freshly prepared. Do not be fooled by fancy claims. Contact long-term aquarists or aquarium societies for their comments and recommendations.

  • Eliminate overfeeding. Meet the nutritional needs of your animals, don't exceed them. Overfeeding, especially with liquid or frozen foods where much waste is incurred, is a sure-fire way of increasing aquarium nutrient level. Keep in mind 90% or more of liquid invertebrate food goes to waste.

  • Excessive use of protein-based foods can quickly add up to a nitrate problem. Pay special attention to animal nutritional needs and feed a variety of foodstuffs.

  • The use of Poly-filter pads is highly recommended.

  • There are various forms of what is termed nitrate-removing media. Denitrifying bacteria colonize this porous material and when placed where aquarium water can flow slowly past it, a diffusion process will slowly over time remove nitrate. However, the process is more anaerobic than anoxic. Therefore even though nitrate is reduced, the processes may be adding further nitrogen-based products such as ammonium to the bulk water. Caution is advised with these products.

  • Calcium reactors should always use a media that is termed 'phosphate' free or at least especially formulated for their use.

  • Aquascaping the aquarium correctly where there is sufficient space between rocks for good water movement will help prevent pockets of detritus.

  • Utilize phosphate/silicate removing media and replace as required.

  • Consider a remotely connected plenum system or refugium.

  • Some aquarists report that by simply placing an airstone in the aquarium it will lessen alga growth. Note that it takes a while before reduction in growth occurs. Carbon dioxide reductions do work for some aquarists.

  • Reconsider the desire to add 'one more pretty fish.'

  • Some aquarists believe that mangroves will quickly absorb nutrients if used in their system. The truth is nutrient removal is quite limited with these 'plants.' They also require additional strong lighting to survive. If the system is already high in nutrients, additional lighting may increase further unwanted alga growth.

  • If the algae-covered rock is worth saving (must not contain any corals/invertebrates), fill a container with seawater to house the rock and add 20 ppm per liter of Chloroquine phosphate. Place the rock in the container along with a small powerhead and in about 10 days the algae should all be dead. Remove, scrub clean, and place rock in a container of new seawater and allow it to soak for a few days before using elsewhere.
  • Diatoms

  • When cleaning brown algae from the aquarium side panels, don't just wipe the viewing surfaces clean by using back-and-forth motion with a cleaning pad. This only distributes the diatoms/silica back into the bulk water where it's used again to produce more diatoms on the surface just cleaned. Instead, place the cleaning pad at the bottom of the surface to be cleaned and slowly slide the pad to the water surface. Then quickly remove the pad and rinse in some clean water. Repeat as necessary. This way, the majority of the diatoms on the viewing surfaces will be 'removed' from the aquarium.

  • As for diatoms on a sand surface, siphon them out if they become mat-like and replace the water removed with freshly prepared seawater. Also, the question sometimes arises why do they keep coming back after cleaning the sand surface. That's because the colonization of nitrifying bacteria in the upper portions of the sandbed in the course of their biological processes produce small amounts of compounds containing silicates. In areas such as the bulk water and sandbed interface, these compounds with the help of light form diatoms, especially during the enhanced activity period associated with re-colonizing the disturbed area. On-going removal of diatom-coated sand should be limited to only the upper most grains. Once the bed settles down, which may take a few months, a conspicuous diatom problem should subside.

  • Tap water, even if processed through an RO system, may still contain silicate. Very few RO units are effective at removing silicate. Even quality RO units remove only about 90% of incoming silicate. To remove all silicate from tap water, one must utilize the proper combinations of resins in well-engineered DI units. Salt mixes should also be tested. Remember, anything that may be composed of silica, e.g., silica sand, Diatomaceous Earth, or decorative rock has a slight solvency at the pH normally found in marine aquariums.
  • Dinoflagellates

  • These free-swimming algae can be reduced/eliminated with the use of ozone or a UV sterilizer. Also, flowing all aquarium water through a sponge filter, which should be cleaned twice a week, is also helpful. And if a quality brand protein skimmer is not being used, it should be as this pest does best in high organic conditions.
  • Cyanobacteria

  • Increase water flow to remove dead spots/low current areas. Use a wavemaker to generate surge, which can prevent the settling of detritus in normally low flow areas, thereby eliminating concentrations of organic matter.

  • Increase or provide efficient protein skimming to help remove the organic nutrients this pest needs to get started and reduce if necessary nitrogen laden compounds such as ammonium and nitrate, along with any excessive phosphate content (very important to keep phosphate as low as possible).

  • Vacuum any/all existing cyanobacteria mats quickly and as often as necessary.

  • Cyanobacteria, including Derbesia and Bryopsis is photosynthetic and prefers the red spectrum. Some aquarists report that after a few days of using only actinic light their cyanobacteria bloom had greatly diminished. Yet get to the root cause!
  • The antibiotic Erythromycin sulfate or Tetracycline will kill cyanobacteria. Even though these chemicals may eliminate this unwanted pest the first time around, further problem blooms may become more resistant to the drugs. It is really much wiser to get to the root of the problem than to put antibiotics into the aquarium. Keep in mind that antibiotics negatively affect system biological filtration. I have used the Boyd product 'ChemiClean' to safely and successfully rid cyano growths. And to keep most systems free of this pest bacterium I have used one tablespoon of 'brown' sugar in my past 180 gallon aquarium once a month. Worked well for me!

The 'Almost' Algae-Free Aquarium

Sooner or later improperly established or maintained aquariums become a fertile environment for unwanted forms of algae and cyanobacteria. It's a far too common happening and one that can be avoided with some forethought. By grasping what conditions might bring on devastating battles with unwanted algae before they actually occur, most of these battles could be avoided. Of course, this is not to say many new aquariums will not exhibit some form of minor alga growth while microbial processes are establishing themselves, however the key word there is 'minor.'

Actually, there's no such thing as an algae-free aquarium. Nor is there an algae-free reef in the wild. Yet it is possible to have a closed system that remains quite free of unwanted forms of algae 'if' attention is paid to understanding the limits of the biological and chemical filtration techniques chosen in relation to the systems bioload goal.

It should be quite clear by now the initial cause of unwanted algae is excessive amounts of the basic nutrients, and once started these unwanted forms of algae become labor intensive and costly to overcome. Therefore it makes more sense to prevent them from gaining a foothold than engaging in all-out war to overcome them once established.

During the aquarium's first few months of performance, different microbial colonies having different functions are forming. While establishing their own equilibrium processes and linking with other microbial colonies, some nutrients may become sufficient enough to generate minor outbreaks of algae. These outbreaks usually have short life spans if biological filtration becomes balanced in favor of using incoming nutrients for energy, rather than them accumulating and becoming stored in the sandbed/rock or bulk water. Sustained plant growth on the other hand is proof there is lack of balanced microbial processes.

In such cases, mineralization and nitrification found in oxic areas and inefficient denitrification processes found in anaerobic areas outweigh (volume-wise) the efficient denitrification processes found in anoxic areas. In simple words, more energy is entering the system then is needed; therefore, it's now being stored in the form of algae. Keep in mind that a skewed microbial system favors nitrogen storage, usually seen in the form of unwanted plant growth, which is actually the storage of those nitrogen compounds! Therefore, systems containing trickle filters, fluidbed filters, incorrectly established sandbeds, and possibly overcrowded with live rock need re-evaluation. Keep in mind, as plant nutrients become more prevalent, algae cells brought into the aquarium on live rock and coral are awakened so to speak. They then either assimilate nitrate and reduce it to ammonium for growth or uptake ammonium directly. When that occurs, more and more green becomes visible in the aquarium. Of course, if green is the favorite color, then who cares. But usually that's not the case.

Furthermore, some aquarists question the value of protein skimming and/or the use of activated carbon. I find that kind of thinking counter to proper system husbandry. Actually, these chemical filtration methods go hand-in-hand with biological filtration, something like bread and butter, and both have already been discussed.

Therefore, first make a decision as to what animal species and quantity will ultimately live in the system. Then choose the filtration techniques to adequately support that bio-load and don't exceed that bioload. Keep in mind, if bioload is increased, i.e., aquarist attempts to stuff six pounds of waste into a five-pound bag, green is very possibly a forthcoming color in the aquarium! Nevertheless, when bioload and filtration techniques are properly match and not exceeded, an almost algae free aquarium is very possible!


Lets now complete Section Four by moving to Chapter 13 and looking at some of those items I like to call - the 'M' words.