By Bob Goemans
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The 'LIVING' Marine Aquarium Manual

Basic and Advanced Husbandry for the 'Modern' Marine Aquarium

by Bob Goemans

Chapter 10 – Seawater Management

Synthetic Seawater

Even though artificial seawater differs somewhat in its mineral composition from that of NSW, it's still a highly suitable solution even for our most delicate species when first placed in the aquarium. Yet, as animal and plant wastes continue to enter, its quality diminishes. Depending upon the relation of the aquariums bio-load to its filtration processes, the deterioration of its quality may vary greatly. Knowing what are 'the' important aquarium seawater parameters, how to test for them and if necessary correct or adjust them, will help immensely in maintaining the health of the system's inhabitants. Therefore, lets begin by briefly discussing salt mixes in general and then proceed to examining some of the aquarium's important seawater parameters and how to 'properly' maintain them.

(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.)

Selecting a Salt Mix

Let me first say there are no 'dry' salt mixes exactly the same, nor are those sold as liquid natural seawater. And there are no brands I know of that would not suffice for the average aquarium, as marine animals appear to be able to adjust to slight variations in water chemistry. And yes, there are often lots of questions as to their quality because of associated, sometimes confusing claims. But when it comes to complex reef aquariums and even nano aquariums that have little in the way of water volume and sometimes containing complex organisms, the differences between brands can become more important, e.g., do they contain sufficient important elements such as magnesium and calcium and/or the more valuable trace elements.

To get answers to that question suggest looking on their label for the concentrations of its important elements and at what level they exist at NSW salinity. If not there, contact the manufacturer for an analysis of their product and if not supplied, could be you might want to look elsewhere for another product that provides this important information. Also recommend occasionally testing newly prepared batches with a quality brand refractometer, especially those solutions to be used for reef aquariums as its calcium, magnesium, alkalinity and pH levels are of extreme importance. If adequate, you may want to stay with that brand, yet, because new products continue to come to market occasionally try a new one and then politely spread the word as to its quality!

Many companies have made major improvements to their mixes over the past decade with some especially made for reef aquariums benefiting from levels of calcium above that found in NSW. Keep in mind higher than NSW calcium content in said salt mixes might result in a white precipitant (snow-like) of calcium carbonate in the mixing container if mixed with tap water already high in minerals. Fortunately this precipitant is harmless and can even be added to the aquarium without concern.

Every once and awhile I receive a question that asks if its feasible to rehydrate the salts that remain from evaporated NSW for marine aquarium use. 'Hypothetically' if all the salts that were in a given amount of seawater were to fall out of solution in their original form, it would be possible to rehydrate and use it. However they fall out in layers as pure water evaporates, and when these dried salts are collected they usually are in disproportionate amounts to what it was when actually dissolved in NSW. Also, due to co-precipitation some compounds will no longer entirely dissolve, which is especially true where metals are concerned. Even though usable to some extent, care and testing is needed to assure that all necessary elements in the correct portions makeup those collected dried salts and therefore mined salts as needed are added before being rehydrated. And yes there are brands, such as Red Sea, that use precipitated ocean salts to make their synthetic dry salt mixes and they appear to have excellent quality control to assure the overall quality of their product.

As to what brand is the best choice for your application, your fauna and flora will make that final decision for you! Nevertheless, contacting other aquarists and/or trusted dealers for their recommendations is also advisable, as is directly contacting the maker of the product as companies these days are highly responsive to inquires about their products. Its also recommended by various companies their dry salt mixes be stirred/mixed for about 2 hours prior to use. As to actual seawater, which is sold in 1 or 5-gallon containers it may be best to aerated for a short period of time before being used, as its been stagnant for a long time. Those shown here are 'only' some of the highly reputable brands available in today's marketplace!

DIY Salt Mix

Because of the availability of many highly trusted and well-blended commercial brands, it's not worth the effort in my opinion to mix your own synthetic sea salts. But that doesn't mean it's not possible! For those that wish to go this road, suggest first reading the formula published in 1940 by Lyman and Fleming in their article titled "The Composition of Sea Water" that appeared in the Journal of Marine Research, No. 3, Vol. 134. And if you do, and decide to give it try, recommend adding some commercially available trace elements to the solution!

Seawater Maintenance

The discussions in this 'Section' have so far laid the groundwork for understanding what can be termed 'the basics' for the liquid that fills one's marine aquarium. As mentioned earlier it may have been a highly suitable solution when first placed in the aquarium, nevertheless as time progresses the composition of said water undergoes chemical changes and some of its parameters change, unfortunately not all for the better! Depending upon the aquarium life forms and abundance, chemical deterioration of its quality will vary greatly. And before one can adequately maintain this solution, more should be known about its inner workings than already discussed. To begin, the following letter, written to me many years ago by Rick Greenfield, president of CaribSea sets the stage for this discussion.

A Day At The Beach

Dear Bob:

Marine aquarium keeping doesn't have to be a battle. If you have ever sat on a tropical beach, you have already seen most of what it takes to keep a trouble free marine aquarium, i.e., sand, water and sky! To a large extent, the degree of difficulty in keeping a marine system depends upon the degree to which the system is balanced with respect to the three phases of physical matter found on earth; gas, liquid and mineral.

In general, the gas oxygen must flux into the system to continue aerobic life and the gas carbon dioxide (C02), a metabolic by product, must come out. Dissolved ionic calcium, must be maintained despite constant precipitation by algae's, corals, mollusks, and buffering ions, and counteract the trend towards lowering pH caused by the nitrification of biological waste. The mineral aragonite caps the pH by chemically precipitating at high pH and, conversely, supports pH by dissolving into liquid calcium ions and buffering ions when the pH drops. All of these factors balance in tropical marine environments in what is variously called the carbonate equilibrium, carbon dioxide system or the seawater buffering system. This equilibrium can be successfully established in captive ecosystems as well but it takes an understanding of the interrelationships of the principle players.

Carbon dioxide (CO2), as gas, is at one end of this equation. It is extremely soluble in water and that is why it is used to make sparkling drinks, sodas etc. This is also why it is such a problem for aquarists because in high enough quantities, and that's not much, it will cause the suffocation of marine life despite adequate oxygen levels. Aquariums tend to accumulate CO2, especially larger systems, lets say over 100 gallons. There are several ways to manage C02. First, you can equilibrate it out with vigorous circulation if you do not have a tight fitting hood. Remember that for the most part, aquariums breathe from the surface. Circulating your system in vertical gyre (circular motion from top to bottom rather than a horizontal racetrack-around the tank type circulation) and visibly agitating the surface of your aquarium with your powerhead output, will speed the exchange of both CO2 and oxygen. This is because the agitation shears the thickness of the surface film created by water tension (called the laminar layer), which allows gases to travel more freely from the atmosphere into the aquarium and, in the case of CO2 from the aquarium water into the atmosphere. Surface skimming and a circulation fan over the top, will also greatly help this process.

Carbon dioxide can also be removed by the photosynthetic action of true plants such as Thalassia (turtle grass) and algae's in all their various forms. Simplified, photosynthesis utilizes carbon dioxide, water and sunlight to produce starch (food) and an excess of oxygen. Plants also simultaneously respire like the rest of us. During the daytime, photosynthesis more than balances the CO2 produced by the plants respiration while enriching the water with oxygen. The drawback to a reef system that relies solely on algae to control CO2 is that at night, algae is respiring without the photosynthetic activity and is therefore a net C02 producer along with the other aerobic life in the system. This causes C02 to build to higher, sometimes dangerous levels at night, which can be traced by the lowering pH (CO2 dissolved in water makes carbonic acid). Corals are even more susceptible to nighttime suffocation as they contain living; respiring algae within their tissues, which they must equilibrate into already C02 enriched water. A recent practice of constant illumination of a sump area planted with algae should neatly handle this nighttime problem and indeed hobbyists have reported encouraging preliminary results.

Another way to handle an excess of dissolved C02 is Kalkwasser. The hydroxyl ion (OH-), of which there are two for every calcium ion, combines with dissolved CO2 to produce a buffering ion with an excess of calcium ion, which is good. Problems with Kalkwasser arise from equating it to a simple calcium additive and ignoring its effect upon the carbonate equilibrium. The addition of Kalkwasser in large batches can have an immediate and profound effect upon pH with consequences to the liquid (dissolved or ionic) portion of the gas/liquid/mineral balance.

The dissolved carbonate ions, bicarbonate and carbonate, are the buffering ions that keep the worlds oceans within narrow pH range and this is what the majority of marine aquarium buffers, alkalinity boosters and 2 part ionic products, effect by direct addition. These substances if not already in a dissolved form, readily dissociate in seawater. The typical marine buffer powder is either totally or primarily composed of sodium bicarbonate ...baking soda (some contain an added carbonate source and a borate). This is a very effective way to quickly raise the buffering capacity, carbonate alkalinity, pH, and stability of a system. It may be just baking soda but it is hard to improve for effectiveness. The by-product is an excess of sodium which, when combined with calcium chloride, adds calcium ions with an excess of chloride ions.

By now you may be thinking "hey, what if I mix sodium bicarbonate or carbonate and calcium chloride together in stoichiometrically correct proportions, wouldn't that supply both calcium and carbonate for my corals? Yes, and this is the gist of the balanced calcium carbonate supplement. The major by product here is an excess of both sodium and chloride, the two primary ionic components of seawater, which effectively raises salinity, but does not create any ionic imbalances to speak of because the other components of seawater are relatively minor. If a manufacturer adds the remaining components of seawater in such a way that they don't react, you will get a residual of artificial seawater. These products are sold in two containers so as to keep the concentrated Ca++ and CO3-- separated and not forming crystals before use.

Now for the mineral phase of the carbonate equilibrium. In normal seawater the mineral formed by the supersaturation of carbonate ions (exceeding the amount of carbonate that seawater can hold in solution) is aragonite, which begins to form at pH of 8.2. This also means that aragonite begins to dissolve at a pH slightly below 8.2 and hence its value as a buffer. Aragonite is a natural biogenic (life formed) mineral formed primarily in shallow tropical seas. Since the formation of aragonite follows supersaturation lets look at how that happens in an aquarium.

One way to supersaturate seawater and grow crystals is to raise the pH above the pH of natural seawater; 8.2. There are a couple of ways this can happen. Kalkwasser will shift pH above 8.2 once it has reacted with all the available CO2. In a well-maintained and well-circulated reef tank, without a lot of fishes, there is not that much dissolved CO2 to begin with. Therefore, the addition of Kalkwasser, especially in batch doses, can have an immediate and profound effect on aquarium pH and degree of supersaturation. How many of you find the water clouding up at least locally after the addition of a large amount of Kalkwasser? That is the formation of tiny calcium carbonate crystals, from the ionic calcium and carbonates present in your aquarium water a direct result of local supersaturation. In highly illuminated systems, the presence of algae or true plants can drive the pH upwards as precipitously as Kalkwasser by the subtraction of dissolved CO2 and the injection of oxygen into the surrounding water as described earlier. The effect is the same. The water has reset to the new pH equilibrium with a lower dissolved calcium level and carbonate alkalinity.

Raising the pH is not the only way to supersaturate. You can also load the system with dissolved calcium and carbonate. Dosing a system, with Kalkwasser, while holding the pH in the normal range by injecting carbon dioxide, requires some accurate monitoring and dosing systems to work, but does allow you to choose the degree of supersaturation you desire. Calcium reactors force the dissolution of calcium carbonate mineral by acidifying the reaction vessel with carbonic acid (C02 dissolved in water) breaking the mineral into ionic calcium and carbonate. Powdered buffers and two part solutions do the same thing but with an excess of some other ions typically sodium and chlorine (the main components of seawater).

There is another way to supersaturate an aquarium and affect its ability to hold the desired pH range and alkalinity. Removing the magnesium ion from normal seawater will facilitate the precipitation of calcite. This can be a great concern as pink coralline algae's are high in magnesium (therefore drawing magnesium out of aquarium water) and some salt mixes are reputed to be deficient in magnesium to begin with. The presence of dissolved magnesium in seawater is what forces the formation of aragonite at a pH above 8.2 rather than calcite at a disastrously low pH of 7.6. In other words, remove enough magnesium from your system and your pH will always be driving towards 7.6, too low to keep most sealife alive.

In knowing all the elements of the air/water/mineral equilibrium, how would that give you some time away from home without a major disaster? First, let's trace what is happening during a total collapse of this chemical balance in your system and how you cause it. A system starts out healthy and stable with the judicious use of one or two of the above-described additives with or without an aragonite substrate. However, with the constant and gradual subtraction of magnesium from the system by the growth of pink coralline algae, decreasing frequency of water changes, and the possibility of magnesium deficient salt mix all conspire to drop the magnesium ion level in a system. With the magnesium level lowered, what was a fairly stable system maintained at a pH level of 8.3 by Kalkwasser, is now less so, and it is easier to precipitate calcite out of a system in the form of crystals so small they are not noticed immediately. As calcite (not aragonite) will co precipitate significant quantities of magnesium, the magnesium drain on a system is thus amplified.

Your test kits are telling you that while you are still above ocean levels for calcium and carbonate ions, it is not as high as it was a month ago and yet you have not changed any procedures. Time to add more Kalkwasser for calcium and a buffer to improve your dKH! But since Kalkwasser is not a very concentrated form of calcium, you have to add a larger quantity than usual to match the buffer (bicarbonate) you have just added. But that larger quantity of Kalkwasser has raised the pH to 8.4. That, along with the higher concentration of carbonate, creates a higher level of calcite crystal formation with the further depletion of magnesium and, since calcite will reach an equilibrium pH value in the mid 7's, in a few days you are below the pH, calcium and dKH levels of normal seawater! This after you just had the system chocked full of calcium, carbonate and a pH of 8.4! ... Time to really hit it. Now you greatly exceed manufacturer's recommended limits of every calcium and carbonate source you can find, all at once. Now all values are really high and you can relax. But in your system the super high levels of calcium and carbonate combined with the even higher pH and even less magnesium has turned your reef into a crystal growing factory. A few days later things aren't looking so good so you break out the test kits again... Hey, what the heck is going on? Also, as if things couldn't get more complicated, you are finally noticing the formation of "chalk" deposits on your pumps, in your plumbing and in between the grains of your aragonite substrate if you have it "clumping."

Now to devise a more stable system based on a day at the beach. Fresh air and moving water get oxygen in and CO2 out of your aquarium. Use Kalkwasser or plants to help if you need to and this is how you check it: Measure the pH of your system in the morning before the lights go on. If it is below 8.0 start devising a CO2 handling strategy. When using additives (manipulating the liquid part of the air/liquid/aragonite system), remember that seawater values of pH and ionic concentration are the stable equilibrium values in the wild and in your aquarium. Strive to maintain these values rather than significantly exceeding them. Pushing these values too far tends to give you an effect opposite of what is intended. Regular partial water changes with a good quality salt mix can keep the water within certain acceptable parameters including the maintenance of magnesium content. This is good advice even when the water looks very clean.

And finally the beach for your aquarium: aragonite. Sit back a bit and let the aragonite substrate do its job! Since the equilibrium pH value of aragonite is the same as seawater, it reacts on demand, automatically, to supply pH and mineral support to a system so you don't have to. All the additives we have mentioned depress the chemical performance of aragonite substrates as they interfere with this aragonite/seawater equilibrium. Use Kalkwasser or plants to control CO2 if you must, and use other additives to make slight adjustments to the water chemistry, but if you are encountering chronic problems with your system, look for a cure rather than masking the symptoms. It may mean changing to intensifying your circulation pattern, adding aragonite, or pedestaling your live rock to avoid detritus accumulation. Many times opening up a tight fitting hood to enhance CO2 degassing or even a circulating fan over the sump can have a lasting effect on the quality and stability of a system. Who knows, maybe you can take a vacation from aquarium problems altogether!


Rick Greenfield

Rick's well-written letter certainly depicts some of the situations that encompass seawater maintenance; yet, there's more that needs to be understood, especially those parameters that directly affect its quality, and therefore its animal health and/or contribute to unwanted growths of algae.


This is probably one of the water parameters tested most often and because of its overall importance could be the most misinterpreted. Since there may be some aquarists that do not fully know what pH means, let's begin with a definition of the water molecule, which is a little repetitive here, but necessary at this point.

A water molecule is composed of two parts hydrogen and one part oxygen. These molecules tend to split into two electrically charged particles, one being the hydrogen +ion and the other the hydroxyl -ion. Stated slightly differently the water molecule (H2O) dissociates or separates into the hydrogen ions (H+) and hydroxyl ion (OH-). This simply adds up to two 'H'ydrogen atoms and one 'O'xygen atom and that equals water. As for pH, it stands for the phrase 'pondus hydrogenii' or weight of potential hydrogen ions. Its measured on a logarithmic scale from 1 to 14. Water is considered neutral if it contains an equal amount of hydrogen and hydroxyl ions, i.e., 7. If there are more hydrogen ions making it below 7, it's considered an acidic condition. If over 7 (less hydrogen ions) its an alkaline condition. And each unit of pH represents a tenfold change in the number of ions present, therefore going from a neutral reading of 7 to a level of 8 means that there is ten times the number of ions present.

Where NSW is concerned, its vast supply of naturally existing buffers can overcome radical changes throughout the waters that surround most of its life forms and therefore stays quite constant at 8.1 – 8.2. Now keep in mind the animals from the wild that are maintained in our aquaria have become accustom to its stability, making it an important maintenance factor in our aquaria. And yes, knowing the meaning of pH and how it's derived is somewhat gratifying. But in closed systems, which do not contain that vast supply of buffering agents found in the wild 'and' often contain high bioloads, it then becomes a must to monitor/test pH. Then understand those results and make the proper decisions as to its maintenance.

Keep in mind during nighttime timeframes, an excess of carbon dioxide is produced by the respiration of plants and animals and lowers pH. Because of that, pH should normally be at its lowest level in the early morning hours. During daylight hours, especially under intense lighting, pH should rise because the photosynthesis process is utilizing carbon dioxide and producing oxygen. A reading of 7.9 early in the morning could be perfectly acceptable 'if' pH climbs to 8.0 or slightly above during the daylight period. If the system experiences such increases and decreases and pH range between night and day remains somewhere between 7.9 - 8.1, then very possibly the system is being managed correctly, i.e., has the proper water movement/gas exchange and calcium/alkalinity and magnesium balances.

Nevertheless, one should keep in mind the ever-present attack on pH from the normal everyday nitrification cycle since it produces some acids/hydrogen atoms in its processes and is almost constantly edging pH somewhat lower!

Keep in mind a pH value as low as 7.7 or as high as 8.5 'could' be considered briefly acceptable under some circumstances, e.g., excess carbon dioxide from various equipment entering system water causing the low level or excess macroalgae in the aquarium causing the high level during daytime timeframes. Yet those kinds of readings would need scrutinizing as to why they were occurring, then brought back to a more reasonable pH level, such as close to 8.0 – 8.2 readings. Drift between daily lows and highs, especially where reef aquariums are involved is another area needing attention. In fact, research is now showing that there is better growth, coloration, and lower mortality of SPS corals when pH drift is minimized, e.g., <.2 per day.

Technically, the ideal pH range for calcification is said to be 8.2 – 8.5, therefore there is some thought that by maintaining a higher pH it serves to hasten coral growth. Nevertheless, the reefs in the wild appear to do well at 8.1 – 8.2, their natural pH range. In my opinion, unless one is performing scientific tests it does not appear to be necessary to maintain anything higher than the natural range for satisfactory growth of corals and/or the proper maintenance of aquarium seawater. Yet - different strokes for different folks!

When it comes to pH in the wild I've recorded afternoon levels as high as 8.9 in tide pools along the Mexico coastline. But the metabolism of creatures in those pools has mostly adapted to wider temperature and pH ranges over the past millions of years. The same is not true for most of the specimens kept by aquarists. I've also heard of pH levels that ranged from 7.4 to 8.7 in aquaria, nevertheless, very low or high pH levels (as mentioned above) and/or large swings in daily low and highs, e.g., >.3, can easily stress most aquarium species.

As for testing pH there are many different brand test kits on the market and all basically use the same reagents. Simply look for a brand that gives clear readings, preferably in 0.1 increments. Test weekly, once in the early morning and again after the system has been well lit for several hours. Keep in mind its better to test your own pH sample, preferably immediately after taking it. Transporting an aquarium water sample to the local store for a pH test may result in an in-accurate reading. Electrical monitors/probes are usually more accurate than titration type test kits, however, they may need recalibrating occasionally. Additionally, their probe needs replacing about every two to three years. And last but not least, keeping a record of your test results is an invaluable source of information, as it can depict trends in the health of the system that may coincide with aquarium related happenings, such as adding too many fish, overfeeding, equipment breakdowns, etc. If so, these now seen 'trends' can then be corrected before they become deadly to the aquariums inhabitants.

If pH is not within NSW levels parameters, it's time to seek the reasons why. Knowing the questions to ask is half the battle. Knowing and understanding the answers is the other half of the battle and these are explained in Chapter 11, Solving pH, Calcium, Magnesium, and/or Alkalinity Problems.

Ammonia (NH3)/Ammonium (NH4)

Maybe I should have titled this subject just 'Ammonium,' as that is the primary algae nutrient. However, it's derived from ammonia, and because of that, lets have a broader look at both.

With that said, unfortunately there are occasions when excess food goes uneaten; something dies and goes unseen and begins to decay; and/or general maintenance lapses. If the present biological filtration capacity cannot completely reduce/oxidize the incoming ammonia to nitrite, then nitrate, ammonia will usually show up on a test kit water sample.

As to just what level ammonia is lethal, that's like asking how much exercise would harm a person who you know nothing about their health. There's also too many variables to make an accurate table depicting toxicity levels for a given species, yet any detectable level should sound the alarm bell! Past research has shown that 0.1 ppm can be lethal for some animals. Others can withstand higher levels, possibly up to 0.6 ppm. But none can continue for long without some kind of damage or continue to process and dispose of their ammonia/ammonium-laden waste products against the backpressure caused by ammonia in solution.

As for ammonia in general, it's really the 'total ammonia' or the sum of free ammonia and ammonium, which are both in solution at the same time. The ammonium ion, which is less dangerous than the ammonia ion, is more commonplace at or near a neutral pH (7.0). But as the pH climbs above neutral, the ammonium ion is converted to the more toxic ammonia and experiences a 10 fold increase when pH moves from 7.0 to 8.0. Between 8.0 to 8.3 it can, depending somewhat on temperature and salinity, increase another 10 fold. This simply means a marine aquarium with a given amount of ammonia would be safer at a lower pH, lower temperature, higher salinity, then the same aquarium at a higher pH, higher temperature and lower salinity. Therefore, whether in new or well-established aquariums it may be wise to first test ammonia prior to raising pH more than 0.1 – 0.2 units per day since pH affects ammonia equilibrium much more than temperature and salinity levels. In fact, it's a consideration the users of Kalkwasser should carefully consider if they are not using carbon dioxide injection equipment to lessen its high pH impact. See calcium in the next chapter for further thoughts on Kalkwasser use.

As for ammonia sources, most comes from animal waste products when they are released into the water column, with some coming from the normal decomposition processes. Should biological filtration in general be adequate, rarely will there ever be signs of ammonia, especially in the 8.1 to 8.2 pH range many hobbyists maintain. Nevertheless, its possible to creep in if the local water company adds chloramine to the tap water. If unsure call your water supply company for information. Of course, overfeeding can cause ammonia spikes even in well-established aquariums, as the already established bacteria quantity is not sufficient to deal with the new higher input of ammonia. In fact, it could take several days for an increase in their numbers to deal with an ammonia spike. Care in not overfeeding cures this problem before it can begin! I've also heard of the homemaker creating an 'instant' ammonia level in the aquarium because they carelessly used an ammonia-based spray cleaner while happily cleaning all glass windows, counter surfaces, etc. in sight near an aquarium! And since these household cleaners contain 'free ammonia,' any aquarium in close proximity can directly absorb the vapor from these sprays. Forewarned is forearmed! And since medications can reduce the efficiency of biological filtration, the result can easily be a rise in the ammonia content.

If experiencing any levels of ammonia, especially in the well-established system, do not add anything that will increase the bio-load and that includes food until the reason for this happening is identified and the cause rectified.

As for testing, there are many different brand ammonia test kits on the market and any of the known brands should suffice nicely. I've even tried the dry strips and for a quick check found them to be quite reliable. And as to testing frequency, recommend it be done once every few months in a well-established stable environment, whether that be a fish-only or reef system. Would also test after making any major equipment changes, and would also check newly prepared seawater (as some generate ammonia) and also after utilizing a medication. And especially so right after some household chores requiring strong cleaning agents were accomplished.

In 'Measures' at the rear of the book there is a table titled 'Ammonia' where, if so inclined you can calculate the amount of toxic/total ammonia (NH3 + NH4).

Nitrite (NO2)

As most hobbyists already know, when ammonia becomes oxidized it forms a compound called nitrite. Even though some hobbyists may still think nitrite is as toxic as ammonia, this is not entirely accurate. The misunderstanding probably came about because the high levels of nitrite seen during the initial nitrification cycle in far past type systems were thought to cause fish damage. But actually, the damage was done during the high ammonia stage and not visible until the brief nitrite period of time. Furthermore, fish actually take in nitrite through chloride cells located in the gills, 'and' since chloride cells have a preference for chloride, the uptake of nitrite in fish is blocked. Therefore, the nitrite level seen in newly started systems is not anywhere near as serious as that of ammonia, providing there are no corals or invertebrates present, which are at risk when nitrite levels are present.

But don't get careless, as this compound if high enough can enter the fish blood stream and oxidize its hemoglobin causing the formation of a product called 'methemoglobin,' a compound the color of chocolaty-brown and which makes it unable to carry oxygen. Methylene blue treatment as explained further on in this work may be of a help with increased oxygenation. Furthermore, anytime there is a finding of nitrite in an established aquarium its an important indicator that an ammonia source is or was recently present and there may be an imbalance of some sort occurring. It's a wakeup call to resolve why this has occurred.

As to that wakeup call, overfeeding is without doubt the most probable cause of minor nitrite readings. The 'fix' to this problem is not always easy to rectify as some hobbyists think their fish need three square meals per day. Would agree some fish such as angelfishes and tangs fair better with numerous small feeding per day. However, in the wild, fishes need to work very hard at getting their required nutrients. They may even 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, fish are certainly not getting the same level of exercise as in the wild. 'Overabundance' of food from the over generous hobbyist can certainly lead to poorly metabolized waste products. When this occurs, it contributes to poor water quality. Therefore, its always wise upfront to understand the nutritional needs of the chosen species, then feed as needed, yet not in excess.

Another cause may be an inadequately sized biological filter or improper water flow (usually too fast) through the various biological filtration media being utilized. Sometimes, this will result in a new system that never seems to fully complete its nitrification cycle! The fix should be easy to put in place, yet could be more live rock/media is needed in relation to the number of inhabitants and amount of food going into the system. This might be one of those cases where a larger unit is warranted, and 'bigger' is better! Medications can also contribute to the causes that bring about ammonia, since it eventually leads to nitrite.

I've also personally experienced slight levels of nitrite when using homemade denitrification devices, such as what I've explained elsewhere in this work. The fix here is an adjustment to water flow, and if a device bought on the market, reread its instructions and adjust according to manufacturer recommendations/or contact the manufacturer directly for help.

As for testing, once a day is sufficient during start-up. After the aquarium has been conditioned, normal maintenance should include occasional nitrite testing. Occasional (in my opinion) is at least once per month. Small levels of nitrite, e.g., 0.1 ppm can indicate problems as noted above that should get your attention. Again, if experiencing any levels of nitrite the safest thing is not to add to the bio-load until the source of the problem is known and resolved. Remember, where there is smoke, there is fire!

Nitrate (NO3)

When it comes to the amount of nitrate in NSW, very little is found especially near fringing reefs, e.g., N03-N = .03 ppm. As you near the shoreline, e.g., lagoons, backwater areas, and boat channels, nitrate readings rise slightly and certain kinds of invertebrate such as soft corals exist without problems. And as you have hopefully noticed in the first sentence, I used 'N03-N' to describe the nitrate level found in the wild. That's because there are two different methods for measuring nitrate, NO3 results in the total weight of the compound/molecule and the other as its nitrogen weight, i.e., NO3-N. And since it's the 'nitrogen' aspect of the compound that is the most important to aquarists, as it's a food source for unwanted algae growth/poor water quality, it's the reading of importance!

And since there are test kits that read either level, one should know how the difference comes about. First, as we all know nitrate is a compound or combination of elements where one molecule of nitrate is composed of one nitrogen atom and three oxygen atoms. Second, it's important to know that the atomic weight of a nitrogen atom is 14.01 and that of oxygen its 16. The reason for that is its total compound/molecule weight is 62.01, therefore the test kit that reads the nitrate molecule will show a reading 4.4 times higher than a test kit that reads nitrate-nitrogen. This means that if using a molecule weight test kit your readings will indicate a level 4.4 times higher than what you should be concerned with, i.e., its nitrogen level! I should note reader letters frequently fail to mention whether their nitrate level was the nitrate molecule or nitrate-nitrogen NO3-N reading. Even mentioning the brand test kit would be helpful. Note, when I refer to nitrate levels in my writings, it always relates to nitrate-nitrogen unless otherwise noted.

As to nitrate in general, prior to a few decades ago very few aquarists were concerned about its levels. Once the emphasis on reef aquariums began, somewhere about the mid-eighties, nitrate became a compound of major interest. Reef keepers quickly became aware that in their specialized ecosystems excessive levels of this compound could cause their animals stress. Additionally, it could generate unwanted forms of algae. The aquarist then began asking what is nitrate, where does it come from, why should it be of concern, when to test for it and how to minimize it.

As to its appearance in our aquariums, it's the end result of the nitrification cycle, i.e., ammonia/ammonium oxidized to nitrite, then to nitrate. In fact, for a very long time many aquarists considered nitrate to be harmless, as levels well over 100 ppm appeared not to bother most fishes.

When more scientific evidence became available it showed that in certain circumstances it could be detrimental to both fishes and invertebrate and that its nitrogen content was a major algae nutrient. Some studies reported that concentrations as little as 20 ppm could cause high mortality rates in certain types of fish fry or their eggs, and various other articles pointed towards some invertebrate having their respiration affected by levels of nitrate between 30 to 100 ppm. Unfortunately there is still not a lot of well-defined scientific data on how nitrate affects most aquarium species.

Regardless, most current information points toward keeping nitrate in the reef aquarium at a much lower level than would be allowed in a fish-only aquarium, e.g., not exceeding 10 ppm in the reef aquarium. For further reading on this subject, review 'Seawater Aquariums, The Captive Environment' by Dr. Steven Spotte. If serious about this hobby, it's a book that should be in your library. Nevertheless, after years of experimenting with reef aquariums I'm convinced best results are achieved by staying under 5 ppm (NO3-N), and highly recommend testing any newly established aquarium 'before' adding any animals. And should its nitrate level be too high, considering a major water change before adding the livestock. Then testing once a week thereafter so as to know what additional livestock and feeding does to the nitrate level.

As for reducing or controlling nitrate accumulation in established reef aquariums, water changes are basically an incorrect approach. This may be fine for the newly set-up system where nitrate may be somewhat high from the initial cycling period. But for long-term control, it's not only not cost-effective, nitrate will flow out of the rock and sandbed interiors, back into the aquariums bulk water over the next day or two. Within a day or two the aquarium's nitrate level will almost be back to the level it was just prior to the water change. As to this compound, get to the root of the problem instead of wasting time and money on water changes. (That's not to say water changes are never needed!)

There are other effective ways to reduce or prevent excessive levels such as maintaining, possibly in a refugium, a healthy growth of macroalgae as it will absorb the nitrate ion and use it for growth. Then, when the macroalgae is flourishing, portions of it can be removed thereby exporting some of the absorbed nitrate. Preventing overfeeding, especially foods high in protein, is another way to lessen/prevent excessive nitrate accumulations. Of course, overcrowding is another cause as it simply results in more food being fed and animal waste products all leading up to higher nitrate levels. The fix should be simple! And there are now chemical means, such as the organic carbon dosing liquids such as vodka, vinegar, methanol, and/or carbon impregnated pellets that can be used in upflow reactors. And these are explained elsewhere in this work. All in all, the control of excessive nitrates seems to be on our doorstep – nevertheless, give much thought as to why it has become necessary!

Salt Content

Lets begin with measuring just how much "saltiness" is in seawater, as there are two broadly acceptable methods - Salinity, and Specific Gravity. A third form of measurement, refractiveness, is gaining popularity as its measuring device becomes less expensive. Another form of measurement, conductivity, is rarely used amongst hobbyists, but is mention here as there may be some interest.


Salinity is the total amount of dissolved solids in seawater, of which 98% is sodium chloride. As for the way its measured, its the total weight of 'dry' salt dissolved in a total of 1000 weight units of water or parts per thousand (ppt). In other words, a pure weight per weight measurement not influenced by temperature. Since seawater is 35 g/kg, it equals 35ppt, with ppt sometimes being denoted as 0/00. As for NSW, its generally 35ppt, but some places differ such as the Baltic Sea (10 – 15ppt) and the Red Sea (40ppt).

When it comes to aquariums, if one wanted to know its actual 'salinity,' a precise weight of seawater would have to be removed and evaporated, and then its remaining salts measured. Not something aquarists want to do, so other methods are used instead. And note, 'Salinity' is the proper unit of measurement to use when one measures the salt content in 'natural' seawaters, as in the wild.

Specific Gravity (S.G.)

This refers to the weight of dissolved solids that are in seawater. If one liter of distilled water and one of seawater were weighed, the one containing seawater would be slightly heavier. As odd as it may seem, if the seawater was slowly poured into a container of pure water and it was possible to keep it from mixing, the seawater would 'sink' to the bottom of the container, with the pure water staying on top.

Specific gravity is the ratio of the density of a sample of seawater at a specific temperature divided by the density of pure water at a specific temperature. And since temperature affects the volume/weight of the samples, its been decided somewhere in history it be tested at 25°C. Most hydrometers have been calibrated at this temperature and many have that temperature quoted on their device, such as the popular plastic swing-arm hydrometers. The more dissolved salts in water the higher its density or specific gravity and the higher in the sample water the arm floats in plastic hydrometers. Distilled water has a specific gravity of 1.000. NSW has approximately 1.025 depending somewhat on where in the world it's sampled, however most reef areas are very close to this level.

Nowadays the old fashion glass floating hydrometers, still available yet some are quite expensive, are easy to break and sometimes difficult to read. The safe and easy to use temperature pre-calibrated plastic hydrometers have become the choice of most hobbyists. In fact, most swing-type hydrometers are thought to be within 0.001 units of complete accuracy. However, they do occasionally need their interior area cleaned of dried salts and their swing arm free of any bubbles when filled to render a fairly accurate reading. There's one company I know of that destroys the mold used to make their hydrometer after a given number is produced and then make a new mold (an expensive process) so as to maintain accuracy.

Depending upon manufacturer, some show both the salinity and the specific gravity level. For most reef aquariums I prefer a specific gravity of 1.024 – 1.026. Sometimes slightly higher if Red Sea species are being maintained, where 1.026 to 1.029 could be considered. And note, 'Specific Gravity' is the proper unit to use when one measures the salt content in 'aquariums.'


There are optical instruments called a 'Refractometer' that measure the refractive index of a liquid, in this case seawater, and then converts that reading into a measurement of salinity. Such instruments are more expensive than the plastic hydrometers noted above, at least a couple of times or more their cost, especially if temperature calibrated. Since a very thin film of water is measured, cleanliness of the testing surface is extremely important. When used properly a very accurate reading is obtained, which would be especially useful when employing hyposalinity as a treatment for some maladies.

Nevertheless, keep in mind most refractometers available on today's market are designed for measuring 'saltwater' (sodium chloride/brine solution), not true seawater! And yes you may say seawater is mostly sodium chloride, but it also contains calcium and magnesium that changes the refractive index slightly, rendering a 'very' slight but incorrect reading. For the aquarist 'purest' with a 'very' complex reef system recommend looking for a refractometer that is calibrated for 'seawater,' and even though its cost is higher it may prevent unnecessary discussions about what brand salt delivers what levels of constituents at what salinity/S.G. and possibly a more accurate and stable seawater environment. Nevertheless most refractometers sold these days are perfectly acceptable for the greatest majority of reef systems.

Also, look for Auto Temperature Compensating (ATC) models, as once calibrated it will auto adjust for environments where the device warms or cools beyond the calibration temperature of 20C, thereby possibly delivering a more accurate reading.


As for conductivity in water, it is the ability of the water to act as a conductor of an electrical current. Pure water will not conduct electricity. But add some impurities like salts or various chemical compounds and conductivity increases. The conductivity of seawater in aquariums can be checked with a conductivity meter. They are usually calibrated in microsiemens (μS/cm) or millisiemens(mS/cm). The conductivity of seawater in millisiemens is about 45 - 48 mS/cm. In microsiemens, it is 45,000 - 48,000 μS/cm. The higher number represents a specific gravity slightly over 1.025, which is more suitable for Red Sea fish and invertebrate. There is no doubt if properly used it results in a very accurate reading of specific gravity. See 'Measures' for a related Chart.

Osmotic Balance

Why is knowing the amount of dissolve salts so important? The answer is 'osmotic balance.' Where marine fishes are concerned, their internal salinity is lower than surrounding seawater. That's because marine fishes 'drink' seawater and purge more salt than they retain via osmosis across the gill membranes. As an interesting side note, the opposite is basically true for freshwater fishes, as they retain the very low levels of salts found in freshwater and internally store it in their kidneys.

Where marine fish are concerned, 'salinity' is actually the more correct methodology because it is the 'amount' of dissolved salts in seawater that fish are working against to maintain its natural osmotic balance. The higher the salt content, the harder it has to work to expel excess salts. If salinity or specific gravity is too high or low, the marine animal may become stressed or may not survive. Yet, even if measuring salinity is thought of as the more correct method, we are not going to change the way it is and measuring specific gravity, the more popular method utilized by aquarists will suffice for our purposes.

To maintain the health of our marine animals it is important to maintain their environment at the correct specific gravity. If you're maintaining a fish-only aquarium, lower than NSW levels will reduce energy requirements for the fishes when purging excess internal salts; reduce stress; reduce the level of aquarium parasites; and, the water will contain slightly more oxygen. How much lower is discussed in Chapter 14.

Element Supplements

Even though all salt mixes provide the necessary ingredients to maintain life, on-going chemical and biological processes utilize some more than others, therefore they need to be monitored more closely and supplemented as needed. There are three 'elements' that are widely supplemented: Magnesium is a major player in alkalinity maintenance; Strontium is an element similar to calcium and utilized in coral growth, and Iodine which is widely used and often misinterpreted and misunderstood. And then there are 'Trace' element solutions that simply contain a variety of elements. Which are really needed? Good question! And even though briefly touched on in Chapter 6, lets focus here on these 'important' supplements.

Magnesium (Mg)

NSW at 35 parts per thousand (1.026 salinity) has a magnesium concentration of 1284 ppm. Only concentrations of the elements chloride and sodium, the two main constituents of seawater are higher. The proportion of magnesium to other constituents is basically a fixed relationship, i.e., ppm relationship is relative to salinity in the wild. A lower salinity, e.g., 1.020, would naturally render a lower magnesium level than what is found at 1.026. At this lower salinity that lower magnesium level would/should be considered optimum. However, there is another 'yardstick' for measuring a correct amount of magnesium in one's aquarium (especially important in reef aquariums), and that is the 3/1 ratio, where magnesium should be three times higher than its present calcium level.

Keep in mind magnesium is a major component of the buffering system, which is composed of carbonates and bicarbonates. In fact, it helps to keep free calcium ions from immediately bonding with free carbonates. It not only influences alkalinity, it also positively impacts the growth of stony corals and is an important component in the most basic microbial processes.

Low magnesium levels can make the maintenance of correct calcium and alkalinity levels difficult, and it also negatively affects calcium absorption. Additionally, slow stony coral and coralline algae growth and turning white/losing coloration is quite feasible/to be expected. Remember, magnesium level should first be related to the systems salinity/specific gravity and/or the 3/1 ratio before any adjustments are considered. Also the accuracy of the test kit (often difficult color-wise to discern correct levels), and precipitation/consumption of this element should be taken into consideration when adjustments are made.

Of course, if salinity/specific gravity were found to be too low for the system's environment, increasing it with a quality salt mix would be the first step before actually increasing its magnesium level. Keep in mind a lower salinity/specific gravity also reduces available calcium and other ions that are so important to overall system health, especially in reef systems. Less than NSW salinity in reef systems does not always make good sense, yet in fish-only systems, its not as important.

Low levels of magnesium can occur for various reasons, such as with either the use of a poor grade salt mix or improper knowledge of how to maintain the carbonate buffering system (alkalinity) the most prominent. Even a high content of coralline algae can cause a low magnesium level! A poor grade of salt mix is the easiest to understand and can simply be rectified by testing a newly mixed batch of seawater and checking its salinity/calcium level, then its magnesium level. Also, high alkalinity and/or pH can cause low magnesium, therefore understanding the alkalinity system, which is more complicated, will be explained in the next chapter.

Since it is known that low levels of magnesium can harm various organisms and higher than NSW levels also have harmful effects on some tested organisms, it doesn't make sense to especially maintain it at far above, e.g., >200 ppm more than what its natural level would be at the systems salinity or the 3/1 ratio. In fact, should magnesium levels become far too high (>1800 ppm), it can cause relaxing of the nerves/block neuromuscular transmissions, possibly seen with snails lying on their sides for long periods of time. Water changes would be the correct approach to rectify the situation.

With much attention to magnesium levels these past few years some hobbyists took it upon themselves to increase magnesium level with the use of Epsom Salts, which is magnesium sulfate (MgSO4) or heptahydrate epsomite (MgSO4 + 7H2O). No doubt great for soaking your feet, but not great for any long-term use in the aquarium. The reason is the makeup of seawater is mostly composed of chlorides, sodium (as sodium chloride), and sulfates; therefore sulfates may increase to un-natural levels negatively affecting the animals within the solution and/or the SO4 interfering with alkalinity measurements. Nevertheless a onetime application would possibly pose no ionic threat to the seawater makeup, but continued use is not recommended because it can skew the ionic balance of the seawater.

For those wishing to make a onetime adjustment it may take about .8 pound of Epsom Salts to raise magnesium 100 ppm in 100 gallons of water. By doing so it also raises sulfate level by about 400 ppm and the level of magnesium by about 8%. Yet, since NSW contains about 2700 ppm sulfate, sulfate levels have risen by 15%. This is nothing the ionic balance of the aquarium's seawater could handle long term!

Magnesium chloride (MgCl2) might be a better choice, yet it can contain some ammonia. Keep in mind magnesium sulfate or magnesium chloride does not contain much more than about 10 - 12% magnesium. However, chloride could be a better choice than sulfate as chloride is present in higher amounts in seawater than sulfates.

Craig Bingman (Aquarium Frontiers on-line, 1999) recommended a solution of 10 volumes of magnesium chloride hexahydrate and one volume of Epsom Salts. He stated that, "the use of this supplement will not appreciably disrupt the ionic ratios of the major two anions in seawater." Keep in mind that magnesium chloride or magnesium chloride hexahydrate are basically the same, as the term hexahydrate simply refers to its water content/ratio of crystals.

Some commercial products combine the magnesium compounds (chloride and sulfate) in ionic-balanced proportions so as to provide a more balanced approach to maintaining magnesium level. Magnesium gluconate is another compound that has been used, however its magnesium content is only about 5% with the rest of the product, a sugar/gluconate, which could cause bacteria blooms if not applied quite slowly/cautiously.

As for those of us not inclined to making their own additives it can't be simpler and safer to use an already prepared ionic balanced magnesium additive and there are currently many on the market, such as those from ESV and Warner Marine. Keep in mind that Kalkwasser does not supply magnesium! In fact, magnesium to some degree will be precipitated near the entrance of that solution into the aquarium, therefore take water samples for testing it far as possible from the entrance of the Kalkwasser solution.

And if using a calcium reactor and lower than desired magnesium levels persist, when changing its media add about 10% of a quality brand Dolomite, which the reactors low pH of about 6.5 will slowly dissolve and help to enhance magnesium levels somewhat.

Strontium (Sr)

There are some in the hobby that are of the opinion some aquarium organisms seem to exhibit better growth when strontium additives are utilized. If so, and they are hobbyist aquarium specimens, what would be an adequate amount, and is it really needed as an additive or can water changes with a quality brand salt mix or other more commonly used additives (as part of their makeup) supply this element in adequate amounts? And since NSW level is 8.5 ppm, is more beneficial? All are good questions. Furthermore, to complicate matters somewhat I've found strontium somewhat difficult to 'accurately' test, even with present test kits and that there is no positive evidence I know of it's a must element to add to have successful growth of stony corals or other healthy aquarium-related organisms.

Nevertheless, in a far past aquarium, exceeding the NSW level generated excessive brown slime-like alga. Yet, comments from some hobbyists that had exceeded NSW limits, even by ten-fold said they did not experienced unwanted algae problems.

As to that past experience, I made my own solution of strontium chloride by using 100 grams of a reagent grade strontium chloride hexahydrate mixed in almost one liter (900 ml) of purified water. As a note of caution if you decide to make your own, use a face shield to prevent any of the mixed liquid from entering the eye in case of splash, and either a dust mask or respirator to avoid breathing any strontium dust. I then used 12 ml of this 10% strontium chloride solution, which is of course is not a 10% strontium solution since it is a combination strontium 'and' chloride, to raise strontium level in a 125 gallon aquarium about 1.0 ppm. Keep in mind there was only about 100 gallons of water in that system due to the volume of live rock, sand, and the fact the aquarium was not filled to the very top.

It was then tested every two weeks, but added strontium every few days. The amount added at any one time greatly depended upon the last test reading. I found it better to divide the amount needed to once again reach about 8.0 ppm, my target, by four which was the number of times I would add strontium over the coming two weeks. Then slightly increased each individual dosage so as to maintain strontium levels near, but not in excess of my goal. After doing this for a few months got to know just about how much was being used daily. Yet, once a higher quality calcium reactor was added to the system, the need for strontium additions seemed to cease. Then stopped its use and saw no difference in the quality or growth of my stony corals.

And yes there is strong evidence some animals need strontium, but it does not appear to be, in my opinion, the type of organisms we keep in our aquariums! Therefore, if still wanting to use a strontium additive, my recommendation is to use a quality test kit and make several tests, and if still thought needed, do not exceed NSW levels!

Iodine (I)

When looking at the wide array of additives for closed systems, iodine additives may be one of the most misunderstood or misused. That's because the interplay of various forms of iodine in the aquarium are either unknown or still somewhat puzzling to many aquarists. And because of that, aquarists in general should have great respect for this powerful oxidizer since misuse can be dangerous or at a minimum no value to aquarium inhabitants.

Since much has been said about the merits of iodine additives, many aquarists simply take that as 'gospel' and sometimes add more than they should thinking more is better. No so! As with anything that will be put into aquariums, questions should first be asked as to how it would interact with what's already in the aquarium. In fact, it would help to at least know the general makeup of the product before using it.

So what are those questions? I see them as better understanding what is iodine, why use it, and what are proper guidelines for its use? Let's begin on how it exists in NSW.

NSW contains approximately 0.06 ppm of iodine (total iodine = iodide (I-) + iodate (IO3)). It's an essential trace element and a powerful oxidant. There are basically five different forms of iodine — iodide, iodate, an organic iodine incorporated into organic material, iodine, and hypoiodate. About one-third of iodine found in seawater is composed of iodide where it is eventually oxidized to iodate by organic matter. Iodide is said to be mostly found above a depth of approximately 500 feet. The other two-thirds, basically iodate, is said to be found below this depth. Other forms exist in minute amounts and/or exist only briefly as transitional products.

Iodine is not stable in seawater. Actually it is considered an intermediary compound with it producing more stable iodide and iodate ions. Iodine quickly reacts with the alkaline portion of seawater (OH-) to form the iodide ion and hypoiodous acid (OHI). Hypoiodous acid undergoes further oxidation-reduction to form more iodide and iodate. What is interesting and noteworthy is that even though the transformation of free iodine is rapid, the same is not true for the reduction of hypoiodous acid. In fact, when hypoiodous acid is finally reduced/oxidized there is further production of iodide and iodate and reduction of alkalinity.

Various organisms such as plankton, micro/macroalgae, bacteria, fish, coralline algae, anemones, sponges and other invertebrate utilize iodine, existing in NSW mostly as iodide and iodate. In fact, sharks can develop goiter-like growths if iodide becomes limited in their diet. As for our personal use, some of us have used Tincture of Iodine on minor cuts to ward off infections. We also use potassium iodide to keep the salt used on our foods flowing freely and our thyroid gland uses it to regulate metabolism. And iodine as potassium iodide has become one of the more common additives used in reef aquariums. Nevertheless, other forms of iodine such as Tincture of Iodine or Lugol's continue to be used even though its value in reef aquariums remains questionable in my opinion.

As to most aquarium additives sold as 'iodine,' they are actually potassium iodide solutions. One of the most noticeable positive effects of iodide usage is on soft corals. Leather corals, mushrooms, and especially Xenia seem to benefit greatly from regular use. Nevertheless the shifting of or incorrect usage of 'iodine species' in the aquarium can cause a wide variety of algae and invertebrate circumstances. For instance; small polyp corals may lose tip coloration, coralline algae may stop growing or bleach, anemones may wander, large polyp corals may contract, sponges may waste away, some forms of unwanted red algae are encouraged, and denitrification processes become slowed. Furthermore, overdosing iodide/iodine products can cause organism enzymes to quickly oxidize it thereby possibly killing both good and harmful bacteria. Keep in mind it's the oxidation process itself that can be dangerous to the organism when it is accelerated or out of control. Yet, too little iodide may reduce cell enzyme activity limiting growth. Therefore, proper usage is extremely important.

Besides a solution of potassium iodide there are two other forms of iodine (elemental iodine) available. One is the common Tincture of Iodine and the other, Lugol's solution. As for Lugol's, which contains 5% iodine, 10% potassium iodide and 85% water, it is commonly referred to as 'strong iodine' or 'Aqueous Iodine' in the U.K.

I started to use Lugol's in 1991 and began administering one drop per fifty gallons per day. Eventually the dosage went to three drops per fifty gallons per day. Soft corals, e.g., leather coral and mushrooms appeared to react very favorably. Unfortunately, Xenia did not respond well at much higher dosages and the additions were stopped in favor of potassium iodide.

It should be noted the iodine portion of Lugol's is 'quickly' converted to iodide. The newly formed iodide and the existing iodide are then converted over a much longer period to iodate. However it's the speed in which the iodine species is oxidized to iodide; anywhere from less than one second to less than a few minutes, that can cause tissue damage at the surface of delicate organisms and/or kill both beneficial and harmful bacteria. That is the reason why the iodine species has value when treating infected corals in hospital tanks. In fact, stony corals infected with white-band and what is referred to as Rapid Tissue Necrosis disease, caused by E. coli bacteria, react favorably to treatments with iodine species (Lugols). Of course, black-band disease is caused by an algae, yet can be treated by immersing the specimen in freshwater. The conversion from iodide to iodate, a less than useful end product occurs over hours/days, e.g., 24 – 36 hours. For general use in reef systems it's the iodide species that stays effective the longest, not iodine.

Even though Lugol's use in reef aquariums is still quite precarious in my opinion, some aquarists have had good success with its use. Until there is much more enlightenment on the benefits/drawbacks of using Tincture of Iodine or Lugol's, I do not recommend using either unless treating specific problem areas.

For those wanting further details see the Eric Borneman article titled "IO-DYIN" in a past issue of FAMA or Craig Bingman's article in a past issue of Aquarium Frontiers titled "The Halogens, Part III: Iodine." I should also add that Dr. Marlin Atkinson, who teaches Chemical Oceanography and Biochemistry of Coral Reefs at the University of Hawaii and who gave a wonderful presentation at the 1997 Western Marine Conference in Las Vegas, also notes the inherent dangers of iodine solutions. He recommends the use of iodide instead of iodine solutions.

As a relevant side issue there has been discussion in the past on the use of Vitamin C (ascorbic acid or ascorbate) to improve organism health in aquariums. It is said some aquarists witnessed improved animal health after dosing their aquariums with Vitamin C. Yet current theory is the improvement seen was caused by Vitamin C converting iodate back to iodide and not that Vitamin C itself had a direct benefit to organism health.

There are also other thoughts and observations concerning the use of iodine. Alf Nilsen has noted he has observed a link between coral bleaching/poor health and the lack of iodine. Mike Paletta notes excessive use of iodine can cause unwanted algae growths. Peter Wilkens has noted the need for iodine in the development of certain pigments in corals and anemones. Julian Sprung has mixed one drop of iodine with some aquarium water and directly dosed Xenia that was about to crash, successfully rejuvenating the specimen. Yet tried on other soft coral, e.g., mushroom coral, it led to some very unhappy specimens.

In the far past have made my own solution of potassium iodide, which resulted in a solution about five times stronger than most store bought solutions. Dosage rate in a previous 125-gallon plenum-equipped reef system, which was far overcrowded with stony and soft corals, was about 5 to 6 drops daily. Generally, that maintained something very close to a NSW level. Yet notice I said 'daily' dose, as I believe this to be better than single weekly doses. And if a store bought product recommends a single weekly dose, recommend dividing that by seven and dosing that amount daily. Keep in mind this type product is quickly acted upon because pH and redox, the controlling aspects, are quickly/constantly changing in the aquarium.

Keep in mind if you make your own iodide solution it is unstable and should not be subjected to high temperatures or bright light. If not sure of the percentage of iodide in a commercial product, contact its manufacturer.

For those that may prefer the plenum style of filtration, it has been found that under anoxic conditions, i.e., a level of oxygen approximately between 0.5 to 2.0 ppm, such as exists in plenum substrates; iodate is converted back to iodide (Bingman, 1997). The reason being is the bacteria in anoxic areas, besides providing highly efficient denitrification, also oxidize/convert iodate back to iodide. This could explain the more vigorous growths of Xenia and other better environmental conditions in plenum-equipped aquariums as the species of choice is iodide, not iodate.

When testing for iodine it is important to know whether the test result is total iodine (iodide + iodate), or that of only iodide. Dr. Atkinson has suggested that when the aquarium's iodide level reaches 0.04 ppm, no further iodide be added until it falls below this level. If the test kit being used reads total iodine, do not add further iodide treatments until the level falls below 0.5 ppm.

The accuracy of test kits for this element is still somewhat questionable, therefore, try a few different brand test kits, and average their results. Consider the average reading a guideline.

Since iodine species are removed by protein skimming and activated carbon, and altered by ozone the aquarist may find it somewhat difficult to maintain proper levels. One thing for sure, aquarists need to adjust additions of this additive to fit their aquarium environment and equipment in use. To error on the low side is much better than overdosing this highly transitional and powerful oxidizer! Nevertheless, it seems like all professional aquarists agree that 'iodine' has become one of the more important elements to monitor, especially in reef aquariums. With a wide array of reasonably priced iodine/iodide additives on the market all aquarists should be giving more attention to this essential element.

Trace Elements Additives

There are many chemical and biological processes that tend to decrease some trace elements and/or trace compounds. There's also just the opposite occurring, as some processes result in a particular species, i.e., element or compound, accumulating. These up or down patterns come from animal and algae/plant activities; others are from the effects of system equipment, such as when ozone is utilized. One thing for sure, there is many diverse nutrient needs and there's no way to test for all possibilities. Nevertheless, to blindly add a broad-based replenisher would be incorrect in my opinion!

Since we do not exactly know how much of these elements are used by the animals and algae in our aquariums, or is removed by activated carbon/protein skimming, care needs to be taken in the use of commercial trace element additives. To complicate the matter, some trace additives may not list or accurately depict the actual quantity of its individual components. In fact, the components listed on the label may be more a good guess than a scientific analysis.

Therefore, when it comes to broad-based trace additives, their need should be decided upon by the condition of one's animals in the aquarium, not product advertising. Diet and water changes are the first two avenues that should be considered if one is leaning towards the use of a trace element replenisher. But if one does decide to supplement their system with trace element additives, highly recommend always beginning by adding only one-quarter of the manufacturers recommended dose. In fact, many aquarists usually find the quarter dose routine to be adequate. Over-dosing can lead to unwanted algae problems and once that is started it is difficult to overcome.

If you decide to begin with the quarter dose method suggested, wait three months before increasing the dosage rate to half the manufacturer's recommendation if the system continues to look good. Should the aquarium continue to be free of unwanted algae for another three months, proceed to the three-quarter dose. If another three months go by without a problem, increase to a full dose. But don't exceed that thinking more is better. It's often not! And I should note, there are many excellent multi-trace element products, such as those shown below.

Test Kits & Record Keeping

Because there are various processes affecting aquarium water, it is wise to visually monitor the aquarium daily (if at all possible) 'and' at least test every two weeks many of the parameters mentioned below. If not, you're playing a guessing game with the health of the aquarium's organisms, and the system in general! In fact, only by testing these important water quality parameters will the hobbyist know 'before' skewed levels have a negative effect.




Carbon Dioxide










Specific Gravity


Keep in mind some seawater parameters are more important than others depending upon the type of system being maintained, e.g., reef or fish-only. However, alkalinity and pH are usually the most important in all systems, with nitrate, phosphate, calcium and magnesium following, with their results dictating what actions will be applied.

In general, the average aquarium test kits are small prepackaged chemistry sets that are easy to use. More complex and accurate versions costing 100 dollars or more are available, but are mostly used by professional aquarists and possibly the upper one or two percent of hobbyists. Even though the lower price aquarium test kits found in aquarium shops, about 50 dollars or less, are not 100% accurate they are far better than guesswork, even that of 'educated' guesswork. Keep in mind certain parameters require more accuracy in testing, e.g., copper. Adjustments to this parameter of only 0.1 ppm could spell the difference between life and death in treating a disease. Yet pinpoint accuracy is not necessary where pH, alkalinity, ammonia, nitrite, nitrate, phosphate, magnesium, iron, and calcium are concerned. Those from a company specializing in test kits or water chemistry aids probably provide the most accuracy for their price and are possibly the better choice.

Test kits use chemicals called reagents, which can be liquid, powder or in tablet form to react with the water sample being tested to provide a needed result. Powdered reagents are sometimes sealed in small aluminum foil pouches (somewhat difficult to pour into a small test tube/receptacle) or in small bottles and if not dated and/or used within two years should, in my opinion, be discarded and replaced with fresh reagents. I consider the usage timeframe for tablet reagents the same. Liquid regents have a shelf life of about one year, yet most are used well within this timeframe. In fact, if not dated recommend writing on their label the date those reagents were received. Regent cost is small but the errors from an incorrect test result can end up being extremely expensive. And keep in mind some test kits contain strong acids or bases and/or some toxic chemicals. They should be kept away from children, and all test kits should be stored in a cool, dark, and dry place so as to keep their reagents from spoiling prematurely.

Most test kits provide either of two forms of testing, i.e., colorimetric or titrimetric. Colorimetric kits result in a color that is compared to a color chip or color chart to indicate the value of the resulting color. Titrimetric test kits use a standard solution, or titrant, which is added to the water sample to produce a change in the color of the water sample. The amount of the titrant used to produce this change is then used to calculate the amount of the substance being tested for, e.g., as in calcium, so-many drops times a given number equal its calcium content. Parameters such as ammonia, nitrite, nitrate, pH, silica, phosphate, copper, iron and iodine are typically tested with the colorimetric method, with alkalinity, calcium, magnesium and strontium tested with the titrimetric method. These kits come with the various needed items to accomplish the test, e.g., test tube(s), eyedropper, graduated measuring container(s), instructions, and the needed reagents.

There are also paper test strips, which when becoming wet with the water being tested will turn a color that indicates a 'general range' of the parameter being tested. Mostly for ammonia, nitrite, nitrate, alkalinity, and pH, these paper strips provide a very quick result, however, they are just that, quick and easy yet providing only a very general result.

Overall, age of the reagent and one's visual perception of colors are the two biggest challenges when it comes to defining a result!

And that's where electronic testing instruments are a great help, as subtle changes in colors, poor quality reagents, or the aquarist having a physical problem discerning colors come to one's rescue. These devices can measure some parameters, e.g., salinity, pH, redox potential, dissolved oxygen, temperature, and even that of calcium and nitrate, and show that result in a digital format. Even though more expensive than the average test kit; they provide quick and accurate results. Keep in mind they are also susceptible to the correctness/shelf life of their calibrating solutions and/or the frequency of those recalibrations.

When it comes to the selection of a test kit, highly recommend discussing the parameters you wish to test with an experienced hobbyist, instead of simply purchasing a 'master' test kit containing a variety of individual test kits. You may find it better to select one brand for certain tests, and another brand for others. And for those kits having glass or plastic utensils, such as test tubes, be sure to clean them properly after making a test. And after washing them in tap water, rinse them with distilled water and place them upside down on a paper towel and allow them to dry without wiping them. Furthermore, always rinse the test tube being used with seawater from the aquarium prior to beginning the test. And when making a test with a liquid reagent, make sure to hold its bottle 'vertically' as this insures the physical size of the drop will be as required to properly accomplish the test. Sideward held bottles often skew drop size, affecting the accuracy of the test.

As for those test results, considered them more a guide. Used regularly, they can help spot problems in the making. Furthermore, it's always wise to retest with another brand before hanging one's hat on a result that appears too far from what's expected. And if it appears to be an incorrect result, check to see it the test kit package has a date or 'batch' code on it, as contacting the manufacturer with this information will help determine if its reagents may still be effective. In fact, if a test appears quite odd, use the test reagents on a sample of distilled water, and if resulting in a reading of any kind, it should be evident the reagents have gone bad.

I should also add that many aquarium shops provide water testing, often at no cost to their customers. Some also sell/provide RO/DI water and/or already mixed seawater, such as my LFS that provides two different grades of premixed sea salts and RO/DI water in the attached photo, which helps to simplify these aspects.

As for record keeping, I cannot remember test results taken months ago, so they are written in a logbook kept near my aquariums. This helps to evaluate water quality trends over the past months and make needed corrections if needed 'before' becoming critical factors affecting the organisms in these aquariums. Regardless of where you may want to keep these notes, e.g., computer or simple notepad, these notes should include date, time of day, parameter name, its result, overall general animal health, percentage of water changes, what new animals were added or lost, equipment changes/modifications, additives used, and any other data deemed useful. Also, consider taking photos of your aquarium, one every week or two, and storing them on your computer so as to add to your 'history' a pictorial aspect.

Over a period of time this 'history' will help recognize trends in one direction or another. And with the help of this book, recognize them for what they are and if needed, correct them. Keep in mind that evaluating trends in water quality is almost impossible 'before' they affect animal health without keeping an on-going record of your aquarium husbandry! Helping to simplify record keeping, you may want to visit, as they can provide services that are tuned to this 'very' important aspect of aquarium keeping!

Finally, when one considers the amount invested in one's overall aquarium, it does not make sense not to have and use an array of different test kits to ensure the quality of its seawater.


Lets now move to Chapter 11 in this Section, where the Seawater Buffering System is discussed. Hopefully, you'll find many answers to questions relating to commonly incurred situations involving calcium and alkalinity along with more hopefully valuable information!