By Bob Goemans
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Real Reef Rock 

Slime Algae (written early 2003)

Authored by: Bob Goemans

It takes many forms and is also called many things, some not printable here. It can be seen as red, black, green, or brown slime-like growths, or in tree-like green forms. All feared and a major nuisance in some aquariums.

One of the most troublesome is a red or black slime-like growth, or what is sometimes called ‘grease algae.’ In the plant world it’s a member of the Kingdom Monera and found in the Division Schizophyta, and is actually a ‘cyanobacteria’ and not an algae.

It begins as a ‘biofilm’ which is nothing more than a very thin film or grouping of microorganisms that have found a home in a suitable neighborhood. Neighborhood preferences are where the current is somewhat slow, an adequate food supply exists, and where there is a preferred light spectrum. It can form on any solid matter that remains in contact with water, even living tissue.

To remain adhered to a surface they synthesize an extracellular polysaccharide that encases the collection site. As the mass increases in size, with both the propagation of its cells and being joined by other new cells, it evolves into a larger more prominent structure called a ‘microbial mat.’

Depending upon the efficiency of the aquarium’s biological filtration in relation to bioload and general maintenance, phosphate can exist in the water column or be available at substrate interfaces. It is the primary energy ingredient that initializes the growth of these unwanted forms of cyanobacteria. Once areas are covered with a film or mat of cyanobacteria, any calcium phosphate adhered to that surface will be reduced, thereby providing the needed energy for further growth. Nitrogen, available in nitrate, nitrite, and ammonium provide the ‘bread and butter’ portion of their diet. All are readily available in closed systems.

In more advanced stages these photosynthetic ‘structures/mats’ become almost 100% a self-sustaining ecology and need little outside input to grow and reproduce. Aquarists generally see it as a red-like slime covering sandbed surfaces, aquarium side panels, and even living corals. Most of the time it’s considered a nuisance because it can get out of control very quickly, however, some very small patches should not be cause for alarm as it is one of the earliest microbial colonizers. Only mat-like growths need be removed.

There’s another cyanobacteria that is commonly encountered and its called ‘Hair Algae.’ Technically its called ‘Derbesia.’ It is often difficult to overcome because aquarists fail to understand its cycle and wait far too long to intercede. Its long, soft and hair-like strands can rapidly cover wide areas. Not only does it become independent of bulk water nutrients once established, trapped detritus/debris can add further nutrients to the bulk water.

It has two life cycles, i.e., as small bubble-like growths and that of an easily recognizable plant-like structure. Tiny spore packages called ‘sporangia’ 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 cells that eventually unite and form a ‘zygote,’ which is the base unit for the growth of a new structure of hair algae. Some aquarists say that hair algae does not grow on surfaces covered with coralline, however, that is not true. Quite frequently the early stage bubbles of Derbesia can be found attached to surfaces covered with coralline, e.g., Sporolithon and Hydrolithon.

Often, aquarists wonder why these growths persist when their nitrate and/or phosphate levels appear to be very low or non-existent. They exist because once established these cyanobacteria growths need little or no nutrients from the bulk water. They simply make their own nitrogen and phosphate needs in and below their base structures with the aquarist providing little else but a preferred spectrum. And, initial growth is usually in an area at or adjacent to a small amount of nutrients found on or in a rock crevice, or on the sandbed/bulk water interface.

Both forms of cyanobacteria are probably easier to prevent than cure. When starting systems its preferable to begin with a sandbed containing a functioning microbial colony before the addition of any nutrient sources, which may include that coming from newly added live rock. Wiser to have nutrient users first, than nutrient sources and no means to dispose of them. However, easier said than done! Another aspect of prevention is the use of a very good phosphate removing media, such as the iron-impregnated media’s. They should preferably be installed at system startup. Once small amounts of phosphate are readable on test kits, system loading/accumulation has already begun. Something like closing the barn doors after the horses have escaped. Live rock should also be well cleaned and cured before placing in the aquarium. That helps, but still can’t guarantee some hair algae spores won’t piggyback into the system. Many times they arrive on coral specimens awaiting sale that have sat in nutrient rich systems. Preventing very low or no flow areas in the aquarium also helps. Spores are much like detritus, and end up where the flow is low. If the neighborhood suits them, its time to build their abode.

Unfortunately, there’s more emphasis on the cure rather than prevention. But, when the need arises, its wise to begin when the first signs of trouble appear. Using herbivores to control minor outbreaks is a reasonable approach, however, in severe cases it only redistributes the waste and further adds to nutrient accumulation. In more severe cases, begin by putting the house in order by siphoning out mats and/or removing by hand hair-like growths. Better to get them small when first recognizable than allowing them to seed the entire aquarium. Then vacuum the sandbed, adjust water movement if necessary, and review feeding and additive use, along with other general maintenance procedures. That includes doing what is needed to maintain phosphate below 0.015 ppm and nitrates below 15 ppm. Since each aquarium is as different as people, its difficult to say just what needs to be corrected and how. But if there is one thing that shouldn’t be done its applying an antibiotic such as Erythromycin sulfate or Tetracycline to kill cyanobacteria. Even though these chemicals may eliminate this unwanted pest the first time, further problem blooms may become more resistant to the drugs. It is much wiser to get to the root of the problem than to put antibiotics into the aquarium. And, bear in mind that antibiotics negatively affect biological filtration.

Even though the battle is frustrating at times, there’s one weapon in our arsenal that is often overlooked, and that is ‘light.’ And no, I’m not suggesting turning off the lights, in fact, I’m recommending just the opposite. You can’t be serious think many as they read this! Past logic has had aquarists reducing the amount of light when a nuisance so-called algae appears. In my opinion, simply another instance of closing the barn doors after the horses have escaped. We are not dealing with plants! We are dealing with structured and highly adaptive microbial communities. Actually, the ‘quality’ of light is a limiting factor, as it has been found that strong light has inhibited or caused harm to cyanobacteria floating near the surface of the ocean.

It is a fact that cyanobacteria prefer conditions where the spectrum is in the red wavelength and intensity is low. Closed systems are well known for nutrient accumulation and with the aquarist often skewing natural seawater constituents in the hope to increase coral growth, quality spectrum is often changed as it passes through the water column.

When it comes to reef aquariums, the goal ‘must’ be to have lamps that generate more of the blue-green spectrum than the higher red wavelengths. Keep in mind there are two wavelengths that trigger photosynthesis — blue and red. For eons coral animals have mostly seen the blue spectrum, as most other visible wavelengths are filtered out in seawater within the first 10 to 20 feet of depth. Plants, algae and cyanobacteria have adapted to the longer red wavelengths. It is the reason why reef aquarists want quality lamps that generate a spectrum mostly in the blue-green range, as that is something most coral animals have used for photosynthesis for zillions of years.

Should the preferred blue-green wavelengths have to pass through seawater that is nutrient loaded and/or contains higher than normal levels of constituents such as calcium or nitrate, the preferred wavelengths are then absorbed/refracted to longer red wavelengths, something algae and cyanobacteria prefer. Checking the age of the lamps is a good first step, as old lamps are usually high in the red band. Next would be the quality of the seawater in the aquarium and if nitrate and calcium levels far exceed that of natural seawater, then make whatever adjustments are necessary to bring it into more natural parameters. Then bast the enemy with quality/intense light! Yet, even this is not the ultimate weapon, but understanding the enemy’s needs and applying corrective steps as systems are begun or age will result in this unwanted entity finding little or no obliging accommodations.

There’s another slime-like ‘real’ algae that is common in many aquaria and that is the brown Diatom algae. It is usually one of the aquarium’s most common colonizers. This type alga can be sheet/film-like or appear as tiny brown dots on the aquariums inside panels. Sometimes it can cover large substrate surfaces when there is sufficient light. Silica/silicate is used in the structure of their cell wall. Depending upon the amount of silicate in solution, the problem can vary in size. When heavily coating objects it can photosynthesize and produce oxygen, often seen as bubbles, which in turn may raise pH to dangerously high levels (above 8.6).

Silica/silicate often enters the aquarium in the tap water used for water changes and/or evaporation makeup. Also, anything composed of silica, e.g., silica sand, Diatomaceous Earth, or decorative rock will have a slight solvency at the pH normally found in marine aquariums. Some aquarium salts also use silica to keep their product dry and free flowing. Many aquarists find it necessary to process their tap water with reverse osmosis and/or deionization equipment prior to use. If in doubt, test the source water before using it.

If cleaning diatom algae from the aquarium side panels, don’t just wipe the viewing surfaces with a back-and-forth motion of the 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’s 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.

Another type of problematic slime-like brown algae is caused by a dinoflagellate. It can result in large areas, including the surfaces of invertebrates, 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 matter. 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. This free-swimming algae is extremely difficult to cure. Silicate is not one of its needs as is the case with diatoms. Unfortunately calcium carbonate is. Since we can not rid the marine aquarium of its calcium carbonate content, 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 quite helpful.

Understanding the needs of the enemy goes a far distance in the battle of unwanted algae and cyanobacteria. It doesn’t mean we are going to win all the battles once they have begun, but if we could prevent the war, then we have accomplished a major objective!

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