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 11 - Seawater Buffer System

At this point in the book highly recommend visiting the 'Glossary' and reviewing the definitions of: carbonic acid; bicarbonate ion; carbonate ion; and calcium carbonate, as they are players in the following discussion on the maintenance of the buffer system. Also, keep in mind in the wild there are almost always sufficient buffering elements/compounds to maintain its pH at about 8.2. Yet in aquaria the necessary constituents seen as its 'alkalinity' are constantly consumed, especially in reef aquariums where its 'calcium' content becomes a major player. With this said, aquarium seawater buffering maintenance is tied to four parameters: pH; alkalinity; magnesium and, calcium. And it is necessary to understand their relationship, then what method or combination of replenishment methods is best for the desired aquarium goals. As for pH, it has already been discussed in length in the last chapter, therefore lets begin here with these other parameters.

(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.)


The word 'Alkalinity' is a general term given the measurement of the buffering capacity of a solution. That is to say it's a measure of the ability of a solution to resist a change in pH when acids or bases (buffers) are added. It should be evident after reading the discussion on pH in the last chapter that seawater is an alkaline solution. Since NSW generally has a stable 8.2 pH, it's apparent it has sufficient buffering elements/compounds to neutralize/counteract the acids that form from different processes within it. In fact, bicarbonates make up about 90% of those buffers, with carbonates making up about 7%.

Nevertheless, closed systems do not have the same buffering capacities as do seas and oceans. Additionally, aquariums usually have a far greater biological load than what is found in a similar size area in the wild. Therefore, 'alkalinity' in closed systems has a natural tendency to decline as it uses up its storehouse of buffers to counteract the acids its life brings about. And without restoring these buffers, aquarium pH will slowly degrade to an unacceptable level, e.g., 7.7 and below. As mentioned above, those alkaline substances or buffers are referred to as its 'alkalinity level.' And especially where reef aquariums are concerned, the wellbeing of its animal life depends upon its keeper's understanding of the buffering/carbonate (alkalinity) system. What does the aquarist do to properly maintain system buffering capacity? Lets begin to answer this very important question by first understanding how to measure 'alkalinity.'

Alkalinity can be measured in three ways: milliequivalents per liter (meq/l), German degrees of hardness (dKH), or parts per million (ppm) of calcium carbonate (CaCO3). The most commonly used and more correct measurement is milliequivalents per liter. It tells us, in molar concentrations, how much acid can be neutralized by a given amount of alkalinity. A less usable expression is one that expresses the German KH sometimes referred to as dKH, which concerns only the calcium carbonate and magnesium carbonate compounds in the system, not the 'total amount of buffering agents' in the system. Therefore, in essence, dKH readings are really more guesswork at what a system contains as a 'totally' usable base to neutralize acid. However, dKH is still a useful measurement and used interchangeably by some aquarists. The conversion for the three units is: 1 meq/l = 2.8 dKH = 50 ppm calcium carbonate.

Another more scientific method of measurement is the mole, or how many ions are in a solution. Let's take water as an example. Water is composed of two hydrogen atoms with each having an atomic weight of 1. Oxygen's atom weighs 16. Therefore, one mole of water is considered 18 grams. Another example would be salt (NaCl). Sodium (Na) has an atomic weight of 23 and chloride (Cl) has a weight of 35. Therefore, they have a gram-molecular-weight, or mole of 58 grams. (116 grams of NaCl would equal two moles.)

Where alkalinity is concerned, one mole of acid will neutralize one mole of base (bicarbonates, carbonates, borate, etc.). To find out how much base a system contains, a titration of an acid must be applied to a sample of seawater prepared with either phenolphthalein (changes to red) or bromthymol blue (changes to yellow). As the acid is dripped into this fixed amount of seawater its pH is reduced. When it reaches 4.5 the seawater sample will change color depending upon which reagent is used. The number of drops needed to bring about a color change is equivalent to the buffer in the system. Hobbyist test kits do basically the same thing. For instance, the Aquarium Systems SeaTesT alkalinity test kit equates each drop to .5 meq/l.

Even though NSW has an alkalinity range of 3.0 meq/l or 8.0 - 8.5 dKH, what range, either in meq/l or dKH is required for good maintenance of closed systems? Definitely higher is the answer for fish-only systems, simply because the closed system is just that with more generally going on chemically in its volume of water than in a similar volume in the wild. As to reef systems, most knowledgeable and well-experienced aquarists prefer 2.5 - 3.5 meq/l (7 - 10 dKH). As for those fish-only systems, 3 - 6 meq/l (8 to 17 dKH) will suffice. Keep in mind fish-only systems have a greater propensity for higher dissolved carbon dioxide levels since respiration from fish and bacteria tend to be higher than in reef systems. Therefore, they are better maintained at slightly higher alkalinity levels, with their calcium levels usually of little importance.

Since aquarium seawater mostly depends upon the aquarist to replenish its buffer content, where does he or she begin to do just that? Of course, the first step is as noted in the discussion on pH in the last chapter, with taking two readings in one day, once a week and recording those readings in a logbook. If the trend is downward, the aeration test as noted further along in this chapter should be used. If an excess of carbon dioxide is not the cause, than the aquarist must look at 'alkalinity' levels and decide how to proceed, also discussed further along in this chapter.

Keep in mind the chemical reactions of the buffer system are constantly shifting to stay in equilibrium with the level of dissolved carbon dioxide driving reactions in one direction or the other. For example, when dissolved carbon dioxide reacts with the water's hydrogen ions, carbonic acid (H2CO3) is formed. That weak acid in turn dissociates into negatively charged bicarbonate (HCO3-) and free hydrogen ions. Carbonate (CO32) is then formed when bicarbonate molecules dissociate, producing free hydrogen ions and molecules of carbonate. Carbonate and bicarbonate remain in equilibrium with each other, both balancing carbonic acid. It can then be said the dissociation of carbon dioxide into carbonic acid, then into bicarbonate and carbonate is the 'alkalinity/buffer system' that maintains NSW at about a pH of 8.2, which contains sufficient 'buffers' to do so without the intervention of humans.

Where closed systems are concerned, biological processes, mostly as biological filtration, producing acids (nitric acid) neutralize bicarbonate ions thereby removing some from the buffering system. Also, some organisms use carbonates and calcium in the formation of skeleton material and/or tissue supports, thus also removing them from the buffer system. As calcium carbonates are used, bicarbonates are neutralized; carbon dioxide levels increase, lowering system pH. Therefore, 'closed' systems need the intervention of the aquarist to replenish these used parameters!

Calcium (Ca)

Besides carbon dioxide, 'calcium' is another important player in the maintenance of alkalinity. Although mostly maintainable in fish-only systems with water changes, it's another story in reef aquariums where calcium needs constant replenishing. One needs to keep in mind that calcium combines with carbonate to form calcium carbonate, either as calcite or aragonite, which in turn can form strong teeth and bones in fish, sturdy stony coral skeletons, mollusk shells, urchin tests, and some support structures in soft corals, sponges and algae. In addition, there's precipitation of this compound on gravel, heaters, impellers on magnetic drive pumps, and even the sides of the aquarium. And once calcium makes this transition, especially to calcite, it is then not easily dissolved at a normal seawater pH, i.e., 8.2, which is at least good for the animals and plants that have utilized the calcium ion in this fashion. In fact, in some heavily stocked reef aquariums, calcifying organisms alone can remove a pound or more of calcium per month; therefore, this and other alkalinity constituents must be monitored frequently.

In the wild, calcium is found at about 400 ppm at a salinity of 1.025, and this, in my opinion, is 'about' where it should be in reef aquaria. In fact, skeleton building will continue to occur when calcium is below 400 ppm if alkalinity is in a balanced or an elevated state, but growth troubles begin when both are too low. Keep in mind a high alkalinity maintains a higher pH, which results in the ratio of calcium and bicarbonate ions being more available for calcification. Yet, for all practicable purposes in reef aquaria a balanced calcium/alkalinity approach and not exceeding 450 ppm for calcium is highly recommended. Actually, exceeding the levels recommended tend to have the opposite results desired! For fish-only systems, a calcium level of 350 ppm is fine.

To prevent undue drops in pH and alkalinity, a balanced state should be maintained between calcium and alkalinity. In fact, there are various online calculators that depict what those levels should be at NSW levels, e.g., a website constructed by Jose Dieck that allows the viewer to choose various products and their amounts to make corrections. Visit his website at:

Balanced NSW Parameters

Alkalinity ----------- Calcium

2.0 meq/l - 5.6 dKH --- 400 ppm

2.5 meq/l - 7.0 dKH --- 410 ppm

3.0 meq/l - 8.4 dKH --- 420 ppm

3.5 meq/l - 9.8 dKH --- 430 ppm

4.0 meq/l -11.2 dKH --- 440 ppm

4.5 meq/l -12.6 dKH --- 450 ppm

Remember, it's not necessary to overreact when seeing calcium fall below NSW levels in aquariums if alkalinity remains at or above 2.5 meq/l. In fact, it might be possible to simply correct somewhat low calcium, i.e., below 380 ppm, with water changes prepared with an excellent salt mix or occasionally with the use of calcium chloride. In fact, many of my past reef aquariums flourished with calcium levels as low as 380 ppm, as long as their alkalinity remained in the 2.5 - 3.5 meq/l range.

In situations where major growth and/or bioload demands create the need for constant calcium corrections, calcium reactors, properly dosed Kalkwasser, or two part solutions can provide a more ionic balanced approach. However, the latter two are more labor intensive and expensive over the long run than reactors. For that reason, I consider calcium reactors the most cost-effective approach in larger reef aquaria and one of the better reef aquarium equipment investments! But keep in mind; adequate calcification does not solely depend upon calcium, as the process requires both an adequate level of calcium and alkalinity! Remember, maintaining the proper level of calcium without having the proper balance of alkalinity does not foster calcification!

When testing calcium level, if the kit provides a 'calcium carbonate' result, it is necessary to divide that amount by 0.4, as actual 'calcium' content is 40% of the calcium carbonate compound. And remember, some test kits are not too accurate when it comes to testing water high in calcium, e.g., over 450 ppm. Therefore, it's recommended the sample be diluted in half with purified water, with its result then multiplied by two to get an accurate answer. There's also a digital calcium monitor available from American Marine that is powered by a 9-volt battery or AC adapter that can be used to measure calcium level.


Even though there are many different aquarium goals, all consume its alkalinity base, i.e., carbonate and bicarbonate ions, because 'life' in its enclosure is producing waste compounds that create acids, which in turn need to be acted upon to keep pH from dropping to unacceptable levels. And in applying alkalinity/calcium supplements, keep in mind what is done to one, affects the other, i.e., when there is precipitation of calcium carbonate, as in calcification, its two components are used in an exact 1:1 ratio, i.e., one meq/l (2.8 dKH; 50 ppm CaCO3 equivalents) for every 20 ppm of calcium. Notice as mentioned above for testing calcium, when the test result is shown as calcium carbonate, actual calcium content is only 40% of that initial result. Therefore, if one were to replace the two components of that compound, one would need to stay with that ratio where its components are concerned, e.g., adding 100 ppm of carbonates/bicarbonates and 40 ppm of calcium. That's exactly what 'two-part' supplements accomplish.

It then might seem that aquarium bulk water calcium and alkalinity could always be kept 'balanced' if a two-part or balanced supplement were used constantly. However, that is not totally correct as unbalanced (calcium/alkalinity) salt mixes, the use of unprocessed water containing various minerals, and/or the adding of balanced supplements incorrectly can skew either of these parameters. In such situations, if calcium content is extremely low with alkalinity in the correct range or those parameter levels just the opposite, a supplement for 'either' carbonates or calcium can be applied to bring it into the correct range. When corrected, then proceed with using a 'balanced' approach for maintaining both of them. Supplements that provide a balanced approach include; two-part solutions; Kalkwasser; calcium acetate; and calcium reactor effluents. Nevertheless, not all are equally effective!

In fact, before any supplements are added to the system it is always wise to test specific gravity, pH, calcium, magnesium and alkalinity. If some results look to be far from normal, use another brand test kit to double check its results. Make sure reagents are not out of date! Keep in mind pH levels affect calcium and alkalinity levels, as the higher it is, the less its possible to raise calcium without it precipitating out of solution as calcium carbonate, thereby lowering alkalinity! Keep goals within the 'Balanced NSW parameters' chart shown above!

To begin this lengthy maintenance discussion, lets first look at the most simplified methods that can be applied.

Water Changes

Periodic water exchanges are a valuable tool in any style aquarium, not only as a means to replenish some buffer and trace elements, but also as a way of reducing the accumulation of waste compounds and/or unneeded trace elements. Nevertheless it's a limited approach, especially in systems having large amounts of calcifying organisms and/or overcrowded/overfed systems. Small systems, such as nano aquariums, that have few fish and little in the way of calcium demanding organisms, such as stony corals and coralline algae, can continue to function well with water changes of 10 - 20% once a month. In addition, highly recommend a 50% water change be considered at least once every six months for these type systems. Yet, where larger more complex systems are concerned, water changes of any fairly good percentage as valuable as they may be, are still inadequate to resolve ever-diminishing alkalinity/calcium levels.

In some locales hobbyists have tap water that is normally high in mineral content. When mixed with quality salt mixes the additional tap water bicarbonates and carbonates help to provide long term buffering. Yet this must be weighed against any unwanted nutrients, such as phosphate, iron, etc., the tap water may contain. Would recommend contacting the supplier of the tap water and requesting an analysis of the incoming water, and also if feasible, discussing its intended use with them.

Calcareous Substrates

There's also some thought calcareous substrates can liberate enough calcium to replace that used in various life processes in the aquarium. It may be true that bacteria respiration in the substrate, especially in deeper sandbeds, generate a low enough pH to dissolve some forms calcareous material, thereby providing 'some' benefit to the above bulk water calcium and alkalinity parameters. Yet depending upon the amount of calcium already in the bulk water as previously discussed, precipitation may occur only in the sandbed causing the sand grains to fuse together. And furthermore, depending upon the biomass in the aquarium, calcifying rates associated with some of its inhabitants and what forms or degree of alkalinity supplementation is in use, calcareous substrate dissolution is more often insufficient to maintain NSW calcium levels.

Keep in mind that minerals such as aragonite are far better than other forms of calcareous material since it begins to dissolve at a pH of 8.2. Unfortunately, aragonite bearing substrates are not globally available, with many aquarists using substrates mainly composed of calcite, which requires a pH of 7.6 or below to begin dissolution. Therefore, materials such as this when used as substrate contribute little or nothing to the maintenance of seawater. It's safe to say that even though 'some' calcium can be liberated from some types of calcareous materials, it is almost always far less than what is really needed to adequately maintain its level in the bulk water.

Two-Part Additives

Another interesting approach is with a liquid product generally referred to as 'two-part balanced calcium and alkalinity' additives. One should keep in mind that when there is precipitation of calcium carbonate, as in calcification, its two components are used in a manner as described above. With this product, there are two separate containers, one having calcium chloride and the other usually a mix of sodium bicarbonate and sodium carbonate, and possibly some other valuable elements. When dosed in equal amounts they provide a natural ionic balance between that of calcium and alkalinity as used in NSW.

However, there are some drawbacks, especially in large aquaria. First, the additives are somewhat expensive, but still very cost-effective for small systems. But in larger aquariums, especially those with large amounts of calcifying organisms, cost of continuing with these type additives could become quite prohibitive. And where this form of alkalinity control remains in use, it may skew the salinity/specific gravity of the water eventually. Keep in mind that 'chloride' and 'sodium' are by far the most abundant ions in seawater, and if these elements are continually added, the water simply becomes more 'salty.' This makes specific gravity vigilance important, with freshwater additions as required to maintain the desired specific gravity level.

These products are sold in separate containers since mixing these concentrated solutions together/in one container would cause precipitation of calcium carbonate crystals, negating their benefit to the system. These separate additives should be applied to the aquarium one after the other, i.e., not hours apart, so as to present a 'balanced' approached of these additions to the system, which use their components quite rapidly. There are also dosers made specifically for automatically dosing two-part solutions.

Calcium Chloride (CaCl2)

This additive is used to increase the 'calcium' content of the water, however it does nothing for the 'alkalinity' side of the equation. In fact if overdosed, i.e., beyond what the present alkalinity relates to as a balanced calcium/alkalinity level, calcium carbonate becomes saturated and both calcium and alkalinity decline/precipitate. Therefore it's wise to raise calcium levels slowly using this type of product and stay within a balanced calcium/alkalinity level.

Notice I said 'slowly' and a way to 'raise' its level. Not maintain it! In past practice using this product I would measure the systems calcium level for several days in a row and average how much it falls each day. No calcium additions were used while gathering this data and three to four days of testing appeared to suffice. I would then daily add double that amount until returning to the desired calcium level. After reaching that goal, a two-part solution was used for its maintenance, not the continued use of calcium chloride. Keep in mind the two main ingredients of seawater are chloride and sodium, therefore long term dosing of calcium chloride may eventually skew its ionic chloride balance. Keep in mind two part solutions are ionic balanced, and this is a much more sensible approach in my opinion to long-term calcium maintenance if a calcium reactor or Kalkwasser equipment is not affordable.

Nevertheless the usage of calcium chloride to accomplish an adjustment is a perfectly acceptable short-term resolution. In fact, more calcium can be added in a much shorter time by using a solution of calcium chloride than what could safely be added by using Kalkwasser. The reason for that is a saturated solution of calcium chloride can hold approximately 160,000 ppm calcium, whereas the saturated solution of calcium hydroxide (Kalkwasser) will hold less than 1000 ppm calcium.

The guesswork as to what some store bought solutions may contain and the fact that calcium chloride in certain forms is quite inexpensive, has led some hobbyists to make their own solution. There are a few ways to approach the 'make-your-own' solution - the use of what is termed more pure grades of calcium chloride, or the use of a very inexpensive common grade that is used for melting snow/deicing roads and sidewalks.

As for the more pure grades there is a reagent 'dihydrate' grade and an industrial 'anhydrous' grade. The dihydrate grade contains 27% calcium and has a pH between 7.2 - 7.8. The anhydrous grade contains 36% calcium and may contain traces of calcium hydroxide that can push its pH into the 8.0 to 9.0 ranges. A third way is with the use of common snow-melting salt.

If the choice is dihydrate, add 600 grams to one liter of purified water. The solution will then contain 160,000 ppm of calcium. If the choice is anhydrous, add 445 grams to one liter of purified water. This solution will also contain 160,000 ppm calcium. One ml of either solution in one gallon of seawater will raise its calcium level by 40 ppm. From there, accurately and safely raising system calcium level is simple mathematics (and commonsense!).

As for the products used to melt snow or keep ice from forming on sidewalks and roads it's usually 98% calcium chloride. Exactly what are its impurities depends upon where the product comes from, but if possible check to see if it contains excessive phosphates or nitrates before use. Some aquarium product companies I know of used it to make their calcium chloride solutions, therefore felt comfortable with their use. Yet in some cases, exactly how much calcium was delivered per ml was guesswork and required some phones calls to resolve. If using a calcium chloride product, hopefully its label will denote the amount delivered per ml, and if not, you need to contact its maker or possibly look elsewhere for another brand.

As for arguments against its use, some say that because of its lower pH (which makes it safer to handle than a solution of calcium hydroxide), it will not precipitate phosphate as does Kalkwasser. Yet, no one that I'm aware of has proven that any significant level of phosphate is actually precipitated 'in' the aquarium with the use of Kalkwasser. And considering the fact that hobbyists should strive to reduce precipitates by using a slow drip rate of Kalkwasser, it then makes sense that a properly dosed Kalkwasser would also reduce any possible phosphate precipitation. Therefore phosphate reduction here is a weak argument. Moreover the misuse of Kalkwasser precipitates the very carbonates that compose the alkalinity system, e.g., magnesium. In all fairness, the misuse of calcium chloride, e.g., if a large quantity were poured into the aquarium, may also precipitate some carbonates. Nevertheless, calcium chloride can be added to the aquarium at a much greater rate than Kalkwasser without precipitating carbonates.

Another weak argument I've seen against its use is that it causes pH to drop into the high seven range during the night and rise during daytime into the low eight range. Well, that's not caused by the use of calcium chloride. In fact, the fall of pH at night and its rise during the day is a very normal process. During the night, plants use oxygen and release carbon dioxide that in turn forms carbonic acid. This weak acid lowers pH. Depending upon various conditions in the aquarium, something close to a pH of 7.9 can be a normal condition early in the morning. During the lighted time frame, plants utilize carbon dioxide and release oxygen, which drives pH up.

The last of the arguments against using calcium chloride is that its use will cause an ionic imbalance sooner or later. Actually, some ionic imbalances may be self-correcting. In fact, there is no evidence that 'slightly' increased chloride levels are harmful. Higher chloride content may even be somewhat beneficial by increasing the solubility and thus the stability of calcium and related ions. Small monthly water changes can keep chloride increases nominal. The key word there is 'could.'

There are really no good reasons not to use calcium chloride to raise a low calcium level 'occasionally.' Simply don't overuse the product and keep in mind the above comments.

Chelated Calcium

There have been several chelated calcium products over the past years, i.e., calcium bonded to another chemical compound, said to make it more biologically available to calcifying organisms. The first of its kind, SeaChem's Reef Calcium was met with mixed emotions when it first arrived on the market many years ago. The thought then was the material used to bond the calcium, a polygluconate, would add too much organic material to the water and possibly hasten unwanted algae growth and/or lower water quality.

From what I understood in those past years was that its gluconic acid neutralized the two positive calcium charges thereby creating a neutral molecule that then contained carbon and calcium. Theory, again as I understood it, said the now neutral molecule could easily pass through cell walls via osmosis, thereby not requiring organism energy that would have required it to acquire a 'charged' molecule. Furthermore the polygluconate, which is a carbohydrate, then breaks down and algae and bacteria use its carbon. The good points here are that calcium in this form is very stable and will not stimulate calcium carbonate precipitation, thereby negatively effecting alkalinity.

Because of some negative comments surrounding this product in those early years I decided to test it in a 20-gallon reef aquarium, which had already been set-up for eight years. For the following two years I used this product for about three months, then stopped its use and utilize calcium hydroxide and calcium chloride for the following three to four months. This aquarium contained my prize specimen of Alveopora that I had at that time for seven years!

There was absolutely no doubt in my mind there was a greater rate of growth in the Alveopora and that of coralline algae when this product was used per the maker's recommendation. In fact, when a slightly higher dose was tried, growth rapidly increased, however, it was a very delicate crystal-like growth. It was so fragile I returned to the recommended dosage rate. In the timeframes when calcium hydroxide and calcium chloride were utilized, growth seemed to considerably slow. During those timeframes I tried to maintain calcium level between 380 to 450 ppm and alkalinity between 7 - 12 dKH. When the chelated product was used, no calcium measurements were taken because the test kit was unable to register a chelated product.

There were also two types of Goniopora in this aquarium and both increased in size during this two-year test period. I should also note this system utilized only live rock for biological filtration and a small powerhead for circulation. It was lighted by two small 15W fluorescent lamps. It never contained any hair algae, but did have some small amounts of bubble algae. Nevertheless I came away from this experiment with being able to keep my Alveopora and Goniopora specimens in a healthy and growing condition, and its reasonable to assume the organic chelator may have been a valuable foodstuff for these type corals.

Controversy as to these type products continue to this day, but I personally had great success with the above named product! FYI - the SeaChem Reef Calcium product is now said to no longer be chelated, as it's now said to be a 'complexed' calcium and most calcium test kits will work just fine when this product is used. For further info on the SeaChem product, visit


These were fully described in Chapter 3, however even though partially repetitive here its necessary for this discussion to repeat some of it --- these mostly cylinder-shaped vessels are filled with calcium carbonate material, usually crushed coral/limestone/aragonite sand, and have carbon dioxide injected into the aquarium water flowing through them. This now acidified water, about a pH of 6.5, slowly dissolves the media or what could be called the reverse of calcification and some dissolved calcium and carbonate constituents' flow in a 'balanced' state when properly maintained to the aquarium. When doing so, these reactors are an extremely good way to maintain the alkalinity system, as Kalkwasser mixing and dosing, expensive two-part solutions and daily dosing, and frequent testing is eliminated thereby providing more 'free time' to sit back and enjoy the beauty of one's aquarium! For a description of this equipment and further discussion on their benefits and disadvantages, see Chapter 3.

Substrate Media

No matter how good the reactor, if the media is of poor quality, the quality of the equipments effluent will be poor! Therefore materials such as old coral skeleton material are not recommended as there is no way to judge their composition content. And materials such as crushed coral, depending upon their source, need special care as to their selection as they may have varying levels of phosphate, iron, and silica, along with a wide range of unneeded trace elements. All of which could result in unwanted growths of algae or other harmful results; in fact, testing the effluent for some of these nutrients is recommended. Also, materials that contain dolomite have far too much magnesium, which when becoming too high in seawater will actually reduce system alkalinity. It's much wiser to stay with well-known brands such as CaribSea ARM or the German KORALlith media, which are among the many on the current marketplace. (contact me for recommendations if needed) A third possibility is crushed coral coming from the Caribbean, as that is mostly aragonite, whereas crushed coral coming from the US mainland is mostly calcite.

Grain size of the media is also important, as too fine, e.g., 2 - 3 mm, will tend to quickly clog as the material melts/implodes thereby reducing water flow through it. Very fine media, which does have better solubility than large particles when new, will become 'mush' within a few months necessitating its replacement. Media grain size of about 5 - 10 mm is generally recommended, and even if it still looks good in the equipment, should be replaced once a year or more often if water tests deem it necessary. Keep in mind when a reactor is used there may be more bicarbonate ions produced than calcium ions depending upon the quality/usage age of the media. Therefore a calcium level below 400 ppm may accompany an alkalinity level higher than what is deemed a 'balanced' alkalinity level. This may cause some hobbyists to increase carbon dioxide flow in hope it will raise the calcium level, however that is often a fruitless approach. The difference between the two parameters will either remain the same or grow larger. If this situation is experienced, it's simply time to replace the media as the calcium ions are becoming depleted.


Kalkwasser (chalk water/calcareous water) also referred to as Limewater, can be utilized to makeup for evaporation and at the same time add calcium and control pH/alkalinity. Wilkins (1973), is credited with the development of the use of Kalkwasser to maintain aquarium calcium and alkalinity. Kalkwasser is most often prepared by dissolving calcium hydroxide (Ca(OH)2) in purified (reverse osmosis/deionized) water. This is a fine caustic powder, almost talc-like, and if inhaled or enters the eye can cause severe tissue damage and when dissolved has a pH of 12, which can cause skin irritation or worse. Another product that can be used to make 'Limewater' is Calcium oxide (CaO), sometimes called Quick Lime. It's somewhat safer and less expensive to use, yet lumpy and more difficult to dissolve. It, however, generates much heat as it dissolves; therefore caution needs to be taken as it could also burn the skin or eyes if mishandled. In the dry forms, both should remain sealed in closed containers until used, as they will absorb carbon dioxide from the air and become less soluble. Both supply the same 'balanced' approach as explained above to maintaining calcium and alkalinity, and besides, they contain magnesium oxide (MgO) and magnesium hydroxide (MgOH), which may somewhat supplement magnesium levels.

There are some benefits provided with the use of Limewater that some other forms of calcium additives do not provide. The most important is the introduction of two hydroxide ions (OH-) for every one calcium ion. The hydroxide ions provide alkalinity by combining with dissolved carbon dioxide, producing bicarbonates and carbonates, and pushing pH higher (preferably maintained in the range of 8.2 - 8.4 when this type product is utilized), which can also help to improve protein skimmer efficiency. The added calcium, in the form of free ions, is immediately available to the carbonate/bicarbonate system and calcifying animals.

Overall, the addition of Limewater increases the demand for dissolved carbon dioxide, either from respiring organisms or that which can 'slowly' enter from the atmosphere when the bulk water tries to remain in equilibrium with the air above it. In fact, the supply of carbon dioxide may or may not be adequate in some systems, especially systems with high calcification rates and/or low evaporation rates. And because pH rises with the reduction of dissolved carbon dioxide, carbon dioxide injection equipment or increased evaporation rates may help alleviate these conditions, which are explained further on in this discussion. In addition, the high pH of the incoming Limewater fluid may precipitate 'some' phosphate as calcium phosphate, and another plus is the solution does not contain unwanted salts such as sodium and chloride.

Bulk supplies of dry calcium hydroxide powder can be purchased in several different ways. It can be bought through chemical supply companies in a very pure 'reagent' grade or a less pure 'technical' grade. It can even be purchased at a grocery store as 'Pickling Lime.' The difference between them is simply the amount of impurities each contains. Of course, many aquarium product companies sell calcium hydroxide under their brand name.

As for pickling lime, it's a human food additive and government regulated in many countries and appears to be suitable for aquarium use. Pickling lime is slightly greater than 95% pure calcium hydroxide. It also contains small amounts of magnesium oxide, calcium oxide, and trace amounts of strontium, sodium, and potassium. Some hobbyists report that aquarium water has a slight yellow color from its use, yet coral continue to do well and pH and calcium levels seem to be stable.

Only about one 'rounded' teaspoon full of calcium hydroxide will dissolve in one gallon of purified water, producing a saturated solution of calcium, i.e., about 900 ppm. The use of processed water is preferable so as to reduce the possibility of unwanted elements/compounds from entering the solution, e.g. phosphate, silica, nitrates, and iron. If more powder is added than what can dissolve, it will settle to the bottom of the container. Generally, a newly mixed solution is allowed to stand for an hour, and then the clear calcium saturated liquid is drawn off and used as soon as possible. Simply adding more water can dissolve any remaining calcium hydroxide powder at the bottom of the mixing container, however, this cannot be repeated too often because carbon dioxide in air above the liquid reacts with the dissolved calcium, thereby precipitating an insoluble calcium carbonate.

The newly prepared Limewater solution should be stored in a tightly closed container and used as soon as feasible. No airstones should be used to stir the mixture, as that would only introduce more carbon dioxide and form more precipitant. The mixing container should be cleaned at least once or twice a week to remove any precipitant. If cleaning does not occur often enough one may think the white power in the bottom of the mixing container was still calcium hydroxide, but not so! Again, if the container is not cleaned often enough, an insoluble precipitate may be added to the aquarium thinking it is the calcium ion. This could very possibly lead to a false calcium reading. A possible indication this was occurring would be a clear slimy gel-like substance on mechanical filtration pads and/or difficulty in maintaining alkalinity.

Control Techniques

Because of its high pH its preferable Limewater is dripped slowly into an area receiving a high water flow. Large amounts added too quickly would swiftly raise system pH, possibly too high, e.g., >8.5 and shock system animals. To overcome this disadvantage there are several ways to proceed to keep system pH within proper operating limits and still supply an adequate amount of calcium to meet most calcifying needs. There are then two aspects that primarily come into play, and they are the amount of evaporation a system experiences each day, and the amount of dissolved carbon dioxide available to help reduce the overall impact of the incoming pH of the Limewater solution.

Manual Dosing

In systems with minor calcification needs its possible to manually drip/pour some Limewater into an area receiving strong water flow to maintain a balanced calcium/alkalinity level. The key word there is 'some,' as the amount added in relation to system pH is quite a limiting factor. Too much Limewater at any one time can cause system pH to quickly climb to dangerously high levels. Also, if evaporated water is automatically replaced with freshwater, the amount of Limewater solution added, especially in small systems may cause a system overflow. If manually applied, space each addition by a few hours; keep an eye on system pH and the systems water level. Feasible, yet labor intensive!

Keep in mind if Limewater is 'flowed' into the aquarium there will be a large area where a too rapid increase in pH is occurring. This increased pH results in the loss of carbonate hardness (buffering capability) since calcium, magnesium and strontium are then precipitating out of solution. Yet if prudently administered, dissolved carbon dioxide in the system's water may have the opportunity to adequately reduce its high pH. At a minimum, thoughtfully applied Limewater greatly reduces precipitation.

Drip/Evaporation Method

When the method first became popular the clear Limewater solution was dripped into an area receiving swift water movement at a rate that would match system evaporation. Keep in mind when first introduced the Limewater immediately reacts with any available dissolved carbon dioxide. If there is insufficient carbon dioxide, system pH can be driven dangerously high. And with most reef aquariums well aerated, there is usually little carbon dioxide available to adequately keep pH from getting too high. In fact, insufficient carbon dioxide is why clouds of minute calcium and carbonate crystals may form when first introduced into aquarium water. These precipitating crystals have to go somewhere and usually end up on the sand grains/live rock or pump housings/impeller shafts!

To somewhat alleviate this situation; Limewater was dispensed during evening hours when systems experienced higher dissolved carbon dioxide levels. Also, increasing aquarium surface agitation with the use of fans helped increase evaporation in some situations. Yet depending upon calcification rates and system evaporation rates, the rate of drip even on a 24/7 schedule did not always supply system need to properly maintain its calcium and alkalinity.

Carbon Dioxide Injection

Then came the carbon dioxide injection method, which is in some ways no different than what is used in the freshwater hobby to encourage the growth of plants. Bottled carbon dioxide gas along with a pH controller and solenoid valve would metered the input of carbon dioxide into the aquarium water to maintain a desired pH level, usually in the range of 8.2 - 8.4. Therefore the lack of sufficient carbon dioxide in the bulk water to adequately compensate for the high pH of the incoming Limewater was resolved. And if evaporation rate and input of the clear Limewater matched system calcification needs, overall system calcium and alkalinity needs were met. Of course the injected carbon dioxide must not be near the area where the Limewater is injected, as that would result in the formation of calcium carbonate crystals and both carbonate and calcium would then be lost before they could properly be used.

Biogenic Carbon Dioxide Generator

There are other ways to generate carbon dioxide than it simply being provided in the bottled compressed form, and that would be by what is called a 'biogenic' carbon dioxide generator, which is simply a 'fermenting' device that operates on the activity of yeast digesting sugar and yielding carbon dioxide and alcohol. It requires more maintenance than a compressed carbon dioxide device and is not nearly as reliable or controllable. If interested, put this topic heading into your web search engine for more information.

Milky-white Method

Even with carbon dioxide injection some systems with very high calcification rates cannot supply enough calcium to sustained growth. Keep in mind 'clear' Limewater contains relatively little calcium, especially when compared to some other calcium supplements. To increase the amount of calcium a clear saturated solution of Limewater would deliver, it is placed into a closed mixing 'reactor' containing an additional amount of calcium hydroxide powder. In the bottom of this mixing vessel is a magnetic stirrer, which when activated stirs its contents resulting in a milky-white solution containing undissolved calcium hydroxide powder. When this solution is delivered to the aquarium, the undissolved powder will dissolve in the aquarium water resulting in an additional amount of calcium being delivered to the system. Again, dissolved carbon dioxide is a limiting factor and this method is best used in conjunction with carbon dioxide injection equipment.

Nilsen Reactor

This is another device using a similar magnetic stirrer as mentioned above, however this mixing vessel is connected to a freshwater supply that is controlled by a float switch in the aquarium/sump. That float switch senses the evaporation rate and when the water level falls below the set level the magnetic stirrer is activated creating a milky white solution of Limewater 'and' at the same time activates a control valve that allows a supply of freshwater to enter the mixing reactor. The chamber fills to the top with its now 'milky-white contents and via an outlet near the top of the reactor flows via gravity to the aquarium/sump. With the only control valve placed in a source of freshwater it stays clear of calcium carbonate clogs and the entire reactor system only needs a weekly cleaning and recharging of the limewater to remain quite functional. Combined with carbon dioxide injection equipment, said method can use various sized reactors, with some quiet large and used at public aquariums to fulfill their needs.

Vinegar Additions

In what appears as a never-ending, yet welcomed thought trend on how to enhance or dispense Limewater into marine systems, there are thoughts on adding white vinegar (Bingman, 1999, 2000), or chelated calcium to Limewater. The thoughts behind this is that the addition of an organic carbon source, such as what is used in the discussion above on 'chelated' calcium additives, or an acetic acid (white vinegar/5% acidity) in small amounts, e.g., 15 ml/gal, would provide additional 'carbon,' which would then become a food source for bacteria who oxidize it, thereby generating some inorganic carbon dioxide. If administered correctly and there is more dissolved carbon dioxide, it could lead to the system being able to contain a greater amount of alkalinity and calcium, e.g. about 10% greater.

There are however some pluses and minuses associated with these suggestions: As to adding the chelated products/calcium acetate, there is concern the additional carbon associated with these products might create unwanted algae growths - a minus. And as to the additions of white vinegar to Limewater, it would help somewhat reduce its high pH and may also encourage additional denitrification in the aquarium substrate thereby reducing nitrate levels somewhat - both a plus. (Keep in mind the acidity of white vinegar varies, so care must be used if trying this method.)

For what its worth there has been some written 'opinions' from aquarists trying the vinegar addition method that said additional coral growth, reduced unwanted forms of algae, and increased skimmer efficiency resulted from its use. In addition there was said to be some sand clumping, possibly caused by increased bacteria growths, as they were easily broken up. Calcified clumps, caused by calcium precipitation would have been more difficult to break up. Another somewhat odd response, and one not yet fully understood that I know of, has been a slimy clear growth on some of the substrate, which was easily removed and stopped forming once vinegar use ceased. All in all, what may work for one may be the downfall of another! Much care is advised if this technique is tried.

Furthermore, to what value these Limewater additions would have in the average reef system is highly debatable and probably, in my opinion, not only more involved than it's worth but could lead to dangerous swings in the balance between seawater's main parameters, i.e., calcium, alkalinity, and magnesium! Yet, if willing to experiment with your reef system, keep detailed records of everything so as to backtrack if necessary, or at least let others know what was done whether successful or not. Share your experiences!

Gerbil Method

Another interesting yet somewhat tricky method to apply Limewater is with what can be called the Gerbil method, which is nothing more than an inverted bottle filled with clear Limewater and securely placed with its opening just touching the systems water level, preferably the sumps water level and an area receiving little or no surface ripples. When evaporation lowers system water level, gravity allows some of the bottles Limewater to enter the water to replace it. A two-liter soda bottle with a small hole in its cap, possibly a length of airline tubing cemented through its cap would suffice nicely. It should go without saying that much care needs to be taken with bottle support so its contents do not accidentally spill into the aquarium water!

Intravenous (IV) Bag

There are also medical intravenous (IV) bags that have a drip control valve that can be filled with Limewater and hung above the tank to slowly administer the solution. Gravity is simply the driving factor in getting the solution into the tank. Keep in mind they have very small dimension tubing and need frequent checking as calcium carbonate will sooner or later clog it. Replace the tubing as needed, or fill the bag with vinegar and allow it to flow through the tubing into a pail, then discard its contents and reuse the bag and tubing without flushing it with freshwater as some remaining vinegar in the bag and tubing is not harmful.

S-K Doser

Another novel approach, said to be invented by two Japanese gentlemen (Matsumoto & Hamanoof) in Tokyo Japan, is a cylinder with an inlet at one end and an outlet at the other end that is partially filled with calcium hydroxide powder. When a float switch senses additional freshwater is needed to makeup for evaporation, a control pump in a freshwater reservoir is turned on forcing freshwater to enter the vertically placed cylinder at its bottom creating a filled cylinder of Limewater and which now flows out the top outlet and then gravity feeds the aquarium/sump to makeup for evaporation. With no air entering the cylinder, little calcium carbonate is formed inside the cylinder keeping the undissolved powder usable for many days before the cylinder needs cleaning and recharging.

Balling Method

This method, named after European hobbyist Hans Balling, requires a sodium chloride free salt, such as what can be provided by Tropic Marin, to which the hobbyist adds sodium carbonate, sodium bicarbonate, and calcium chloride in the correct ratios such that the sodium and chloride is in the same ratio as in the wild, - with the calcium and bicarbonates also added in the correct proportions but at higher concentrations. By using a sodium chloride free salt for water changes, it basically reduces the excess of sodium and chloride ions that are in the three additives mentioned above. In other words, the mix used for a water change is basically one large 'two-part' additive! Nevertheless, in the long run an ionic imbalance could result. In fact, some magnesium chloride or strontium chloride could be substituted for some of calcium chloride. Altogether feasible, its labor intensive and requires careful measurements of all ingredients. For more information on this process, suggest going to your favorite web search engine and looking up the 'Balling method.'

Calcium Blocks

As for calcium blocks, there are a few different brands to choose from. They appear to be a blend of calcium sulfate (plaster of Paris/gypsum), calcium chloride, and maybe some additional trace elements. Simply dropping one or two blocks in a sump or a rear corner of an aquarium helps to supplement the calcium level. Depending upon water movement where the block is placed and/or how fast calcium is being used in the aquarium, these blocks can be useful; nevertheless, their use is probably more suited for small aquaria where calcium demands are often fairly low.

Separate Buffers

There's no doubt that there are many fine products sold as buffers to enhance the buffering capacity/pH/carbonate alkalinity of aquariums. They certainly have their place in our arsenal of products to help maintain quality seawater. Many basically use sodium bicarbonate (NaHCO3) - baking soda as their ingredients, yet some also add small amounts of sodium carbonate (Soda Ash) or/and sodium tetraborate (Borax) to enhance their products. As explained in the last chapter in the letter titled 'A Day At The Beach,' their misuse can cause mystifying pH and calcium swings, especially to those fairly new to the hobby.

If a commercial buffer is chosen (usually mostly sodium bicarbonate - baking soda), use a well-known brand name, use sparingly, don't rush level adjustments, and never exceed dosage recommendations. Remember, if encountering perplexing or persistent problems look for the root cause, not temporary solutions (forgive the pun).

As for the commonly available baking soda, it will not raise pH higher than 8.3, yet still needs to be handled with some forethought. And keep in mind long term dosing of sodium-based compounds may eventually skew the ionic balance of the seawater. (Go back and read 'A Day At The Beach.')

Testing Calcium

The calcium level being maintained is measured as ppm of the calcium ion (Ca++), and not calcium carbonate, and was fully discussed above. But as to how often to test, it depends on the aquarium environment and possibly how long the system has been established. Calcium levels can remain fairly steady in newly established reef systems. Yet well-established reef systems with heavy growths of coralline algae, numerous stony corals, clams, and even some soft corals that require calcium, quickly deplete its level. In new reef systems, testing every two to three weeks may suffice. With well-established reef systems recommend testing weekly. In fish-only systems, calcium level need not be tested if experiencing reasonable and periodical water changes. Furthermore, magnesium levels do not influence calcium test kit readings, as what is seen in the test result is an accurate reading of the calcium present.

The Aragonite Solution

When purified water is used for water changes or evaporation makeup, it contains no calcium. And its pH, especially that of reverse osmoses and deionized water is usually quite low, e.g., 6.5 - 7.0. Now take into consideration the aragonite particle enters a condition of equilibrium at a pH of 8.2. That is to say it begins the reversal of the very process that originally formed the particle and starts to dissolve. This can be quite beneficial as the aragonite particle is about 97% calcium.

Most of us have seen calcium reactors where carbon dioxide is used to lower pH to a point where the water becomes acidic enough to dissolve its calcareous gravel. But, what if you didn't need carbon dioxide to accomplish a modest dissolution process. Therefore why not use reverse osmoses or deionized water to dissolve some aragonite gravel in a storage container. Water with such a low pH is an excellent solvent for almost any type calcareous gravel. Yet aragonite, because it's so pure, is a much better choice than crushed coral or oyster shell and contains much less phosphate than other forms of calcareous material.

I should note this method is not for maintaining the calcium level in a reef aquarium. It is simply a process by which the water that will be used for evaporation make-up or water changes will be 'enhanced' prior to use. I use about 50 pounds of aragonite in a strong plastic container that in turn holds about 35 gallons of reverse osmoses and deionized water. When water is needed for my aquariums it is drawn from this container and what is remaining is topped-off with fresh reverse osmoses and deionized water that is stored in other large containers. I have found the enhanced water to contain somewhere between 50 to 100 ppm of calcium and have a pH of 8.4. I want to thank Leo Wojcik with Marine Technical Concepts for this idea.

Solving pH, Calcium, Magnesium and/or Alkalinity Problems

First, be doubly sure you have what's perceived as a problem to really be a problem before trying to correct it! Test, then test again with possibly another brand test kit before making thought to be needed corrections. Then, using what is discussed above as the 'balanced' state of alkalinity and calcium levels, do not exceed either, with staying somewhat in the middle of these acceptable ranges at the NSW pH range.

In fact, when it comes to adding any product that affects water chemistry, there are some questions that must be answered before being used, e.g., are the products instructions clearly written/understandable, are its ingredients listed, and does the manufacturer provide contact information. If not, unless you're an expert in the field of water chemistry, its like playing Russian Roulette! One bad move and much sorrow could follow!

High pH Values

Generally, high pH occurrences are rare in aquaria. Nevertheless there have been reports of aquaria having a large presence of macroalgae where pH temporarily reaches 8.5 - 8.6 during intense lighting periods. The key word there is 'temporarily' as this is not detrimental. Yet if this level persisted throughout the day it should be considered risky, and furthermore the shift between night and day could be overly extensive! The safest way to correct such a situation is remove the excess alga causing the high pH situation to prevent a reoccurrence.

If the aquarium has little in the way of excess algae, and pH is daily running higher than desired, e.g., 8.4 - 8.5, there is very possibly a shortage of dissolved carbon dioxide. In systems using Limewater, pH can sometimes run higher than an acceptable high level of 8.2 - 8.4. Increasing gas exchange at the surface of the aquarium, increasing carbon dioxide injection, adding some organic acid such as vinegar (directly to aquarium sump water or to the Limewater itself) and/or 'not' lighting an algae refugium at opposition times of the main system if so equipped, are ways to correct this situation. But keep in mind; any corrections should be done 'slowly,' i.e., over a period of a day or two.

For those systems dosing Kalkwasser/Limewater, keep in mind its pH is about 12! Overdosing can quickly raise pH, therefore check the amount entering the system and if need be reduce the amount being dosed and/or dose only during evening hours when the aquarium's carbon dioxide level is normally higher. A slow drip of vinegar into the Limewater will also reduced its pH.

It might be much wiser to only dose Limewater throughout evening hours and use the calcium reactor only during daytime when the system's pH tends to naturally rise, somewhat offsetting the reactors effluent pH of about 6.5.

Reef systems with tight fitting aquarium covers and inadequate aeration, e.g., no protein skimmer, are actually starved for free carbon dioxide that is needed to supply the necessary buffer carbonates and bicarbonates. This results in the bulk water always having a high pH 'and' poor calcification. - Remove covers and increase aeration.

And yes there are pH-reducing additives, and/or that of dripping swimming pool Muratic Acid into the aquarium sump water, but its much wiser to get to the root of the cause than simply reducing the high pH by using these methods! And of course, its always wise to double check the pH level with another test kit or calibrate a pH probe before adding anything to lower pH. Keep in mind that sudden drops or even that of raises in pH, can shock the animals in the aquarium! Again, rarely are there high pH problems!

And keep in mind, the actual level of calcium and alkalinity are dependent on pH, as the higher it is, the less its possible to raise calcium without it precipitating out of solution, thereby lowering alkalinity! For example, if pH is 8.1 - 8.2, and calcium is about 390 - 410 and alkalinity is 5 - 6 dKH, the system 'is' balanced!

Low pH Values

Most aquariums tend to see a slipping pH for several reasons. As for pH parameters in a fish-only aquarium, something in the range of 7.7 - 8.2 is totally acceptable, especially for those systems with a high bioload. And daily swings of slightly more than .3 is also acceptable, however one should consider using a high quality protein skimmer as a way to increase oxygenation, especially during evening hours thereby helping to minimize the swing.

Where reef systems are involved, it's more involved and there are several reasons why pH tends to drop. Probably the first and foremost is the bioload is too large for the size/volume of the aquarium. All organisms use oxygen right down to the smallest, e.g., bacteria, and the more fed, the more waste to break down thereby creating a larger demand for oxygen. - And then there are algae, which use oxygen and give off carbon dioxide during the night (just the opposite during the day) - Then there's the water surface where carbon dioxide escapes and oxygen is hopefully gained 'if' there is sufficient surface agitation and the surface is open to the air in the room. - And if a quality protein skimmer is not being used, the system is missing out on an excellent way to drive off carbon dioxide and gain oxygen. - Then there's water chemistry, and if calcium, alkalinity and magnesium are not in balance, then serious pH drops can occur.

Therefore, if pH is 'thought' to be lower than desired or below 7.8 'and' calcium and alkalinity are as mentioned above, the following situations should be reviewed.

1) If the aquarium is somewhat new, less than 6 months old - maturing bacteria and algae colonies put demands on the system's ability to maintain a stable pH range not normally seen once the system stabilizes. Small weekly water changes for the first few months will help renew the carbonates and bicarbonates used up. Also, the fulltime use of a quality protein skimmer, a good tool for increasing dissolved oxygen levels, will also help the system get by the maturing process. Simply keep in mind not to allow bioload to grow too quickly in new systems, as it will greatly negatively impact pH possibly causing one to overreact to what is perceived as a low pH problem! During this timeframe highly recommend not overreacting by adding unnecessary additives/buffers.

2) High fish load and/or poor aeration - carbon dioxide accumulates and drives pH lower. If no calcifying organisms are present, the sole addition of a buffer might suffice, as it will pull the excess carbon dioxide into the buffer system, however it will also tie up/precipitate any free calcium (drive calcium lower). But in a fish-only system this should not be a problem.

Keep in mind all organisms in the aquarium need oxygen, even algae (at nighttime) and bacteria. As to feeding, the food fed is used for biological processes/growth that require oxygen. Uneaten foods and animal waste feed smaller organisms and so on down the road to the bacteria level finally generating nitrate. Each one of these paths takes oxygen from the system affecting the balance between oxygen and carbon dioxide. The larger the bioload, the more is fed and the larger the demand for oxygen, which negatively affects pH. The fix would be to lower the biological load (best approach) and/or increase aeration, e.g., upgrade filtration system equipment/protein skimmer. Maybe a larger aquarium without increases to existing bioload if reducing present bioload is out of the question! Also, possibly increasing the volume of water changes and/or decrease the time between them would be another aspect to try. Nevertheless, as long as calcium and alkalinity levels are somewhat above that found in the wild and/or 'balanced' as shown above, (and magnesium is at NSW levels) calcification rates will continue to be acceptable with a pH as low as 7.8.

3) Excessive carbon dioxide dosing - besides driving down pH it may also enhance algae growth, especially in aquaria containing a large bio-load that is associated with nutrients such as phosphate, nitrate and possibly insufficient herbivores. The fix requires checking the effluent of the devices using carbon dioxide, such as a calcium reactor and correcting its supply if needed. Limiting calcium reactor use to only daytime periods may also help, as that is when pH normally rises, and if Limewater additions are being used apply solely during evening hours as that liquid has a high pH.

4) The room containing the aquarium may have air that is above the normal carbon dioxide level found outside of the home. - This sometimes occurs during the winter season when in colder climates rooms are shutoff from outside air and inside carbon dioxide levels rise due to lack of circulation with outside air. Corrections include an algae refugium lit at opposite times of the main system, supplying an 'outside the home air supply' to the protein skimmer (If using inside air, the skimmer simply injects it into the aquarium creating carbonic acid somewhat neutralizing the buffer system!), employing a sump-located aerator, opening windows if feasible, or carefully adding a buffer supplement.

5) To help reduce the slide of pH during unlit evening hours, refugia containing an abundant growths of algae and lit at opposite timeframes from the main system is an acceptable approach and was explained in Chapter 8.

6) Inadequate aeration - poor water movement/gas exchange retains more carbon dioxide, therefore increasing the amount of carbonic acid resulting in pH declining. - Try to have good circulation in the aquarium, e.g., carbon dioxide laden water lower in the aquarium is directed upwards and oxygen rich surface water is directed downwards, as that greatly helps gas exchange. It may also suspend detritus making it easier for it to be removed by good protein skimming and/or other filtration equipment thereby lessening the bacteria oxygen demand for its breakdown. Having a quality and properly operating protein skimmer is also a very good way to increased oxygen in the system, especially during evening hours. Also, if the aquarium has a cover it should be removed or ventilated with small fans so that outside air is constantly flowing onto the top water surface of the aquarium.

7) Low pH becomes a constant problem, and/or there is a large swing between low and high-level pH readings - there could very well be a magnesium shortage. Decreasing levels of magnesium are caused by salt mixes deficient in magnesium; less and less water changes with a quality salt mix; the growth of coralline algae; or precipitation. Low magnesium levels push pH even lower, precipitating further calcium in the form of calcite/magnesium. Maintaining magnesium in its proper range will help in the formation of aragonite, not calcite and help to naturally buffer the system. Keep in mind the NSW dKH is about 8.0 - 8.5 (3 meq/l). If magnesium falls below its NSW level of 1350 ppm, it becomes difficult to maintain calcium and dKH no matter what methods are used to boost or maintain them! That's important because alkalinity is directly linked to pH swing. Therefore maintain magnesium at about 1350, with calcium and alkalinity in a balanced state as discussed above at 35ppt salinity, and swings will then be greatly minimized. As to a higher alkalinity, e.g., 10 - 12 dKH along with an increased balanced calcium level, it has been seen to further stabilize pH drift, however, there is the possibility of brittle skeletal formations in some small polyp stony (sps) corals, and possibly other negative situations not yet defined.

8) Buffers – Keep in mind a pH buffer that is solely Sodium bicarbonate (NaHCO3)/Arm & Hammer/Baking Soda) will not 'raise' pH other than a very minor amount and then for only the first few hours after its use. What it really does is increase the dKH level, thereby buffering the pH against going to a level below its already existing lowest early morning (unlit timeframe) level. Actually, baking soda makes up most of all store-purchased buffers, however some have slight additions of sodium carbonate (Washing Soda), which 'will' raise pH. Keep in mind it may take a day or two for pH to stabilize when these type products are used, so do not add too much at any one time. Follow their instructions. Remember, it is easy to shock the inhabitants in the aquarium, especially invertebrate as they are more sensitive than most fishes. And be sure of product contents before used!

Furthermore, while adding buffers may seem somewhat beneficial, it will if use continues increase the sodium ions in the water and thereby slowly increase the imbalance between alkalinity, calcium, and magnesium. Remember, affect one, affect all. In fact, many aquarium service companies use baking soda to bolster dKH/alkalinity because it is not only effective for this purpose, but also much less expensive than commercially prepared buffers. Yet, some store bought buffers also come with small amounts borate/Boric acid that further helps to stabilize pH. Nevertheless the real solution, forgive the pun, is to get to the root cause of the problem and then correct it!

FYI - As a matter of information there are two elements that have a positive effect on pH - Boron in the form of inorganic borate, and carbon in the form of inorganic bicarbonates. Keep in mind that carbon dioxide in the air can be absorbed at the aquariums water surface as inorganic carbon or from animal and plant respiration in the water as organic carbon. Since inorganic carbon is more molecularly available than organic carbon from the decomposition of animal waste, it quickly reacts with dissolved metals/boron in seawater to form inorganic bicarbonate. In fact, most of the inorganic carbon in average seawater is in the form of bicarbonate, with the remainder as carbonate. Unfortunately carbonate is mostly unstable in seawater and can readily combine with dissolved calcium, magnesium and some trace elements and precipitate out of solution. As for boron, it accounts for about 10% of the buffering capacity and is present mostly as borate (B(OH)4).

Should none of the suggestions above correct a problematic pH, then one must look at the accumulation of organic acids and phosphate compounds, which are quickly cycled in the wild but no so in closed systems. Keep in mind the nitrification cycle naturally creates some nitric acid, which in turn drives pH lower. And should a system be overcrowded/overfed, have dirty/clogged substrate, and possibly a poorly performing protein skimmer and/or dead or dying animals and plants, an overburdened nitrification process would be a drain on pH. On the other hand, denitrification does just the opposite as it dissolves calcium carbonate and tends to drive pH somewhat higher. Nevertheless, most marine aquariums have more biological area devoted to nitrification than denitrification. The only systems that possibly have a greater percentage of denitrification would be those with Jaubert plenum beds. However, this form of biological filtration has never become too popular as explained in Chapter 8. Furthermore phosphate, usually plentiful in closed systems, combines with calcium and magnesium to form compounds that precipitate out of solution, thereby removing these valuable components of the buffering (alkalinity) system. And as explained in #2 above, a dropping pH can only be cured with improved maintenance/water changes or the reduction of bioload, as the addition of buffers (carbonates and bicarbonates) will only be a very temporary fix.

To help judge which of the above, i.e., poor gas exchange or an over abundance of organic acid is causing an unsatisfactory pH in your aquarium, i.e., <8.0 and remain there, there's a simple way to accomplish that. If pH hangs below 8.0 (if above, these tests are not needed), simply take a small amount of water from the aquarium and aerate for twelve hours. Then test both the aerated water and that of the aquarium with a pH test kit. If the aerated water has a lower pH by more than 0.1 units than the aquarium bulk water, the bulk water may have excess carbon dioxide and improved water circulation is advised. Said improvement may take a week to ten days to show an improvement. However, if this is not the problem then 'alkalinity' must be adjusted with a carbonate buffer, and adjustments should be limited to no more than a 0.2 - 0.3 rise per day. As explained in Chapter 14, rises beyond this will adversely affect fish health.

Keep in mind the 'ideal' pH range for calcification is between 8.2 - 8.5, and there is some thought by some aquarists that by maintaining a higher pH than in the wild 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. Therefore, unless one is performing scientific tests it does not appear to be necessary to maintain anything higher for satisfactory growth of corals and/or proper maintenance of seawater, at least in my opinion.

Bottom-line, use up-to-date reagents/calibrated probes, test correctly, keep calcium, alkalinity and magnesium in balance, and there will be few issues to resolve where pH is concerned!

Calcium and/or Alkalinity Problems

If both are above the balanced state, then do nothing until their levels return to the balanced state, as calcification will drive them lower. If one falls to below what is considered to be in the balanced state, than add only 'its' two-part component until again appearing in the balanced state.

If solely raising alkalinity, no matter what product is being used, its best to keep pH from rising much above 8.3 when being applied as anything higher may precipitate calcium until the system is again in a balanced state. If already 8.3 it may be best to simply use baking soda (sodium bicarbonate) as it will not raise pH much further than this. Commercial alkalinity buffers may combine baking soda with some sodium carbonate (Washing soda), possibly in a six to one ratio, which can push pH higher. Therefore store bought buffers, if used, require careful pH monitoring and should be added sparingly and given sufficient time, e.g., at least a day to react before adding a further dose. Once alkalinity is back in the balanced state with calcium, resume a two-part/balanced approach. Its been said one can make their own 'alkalinity' buffer by mixing six parts of sodium bicarbonate to one part sodium carbonate, and applying as mentioned above. Nevertheless, some already prepared commercial buffers have some added valuable components, e.g., magnesium and boron, and therefore highly recommend going with a well-known brand instead of making your own buffer.

Keep in mind if adding a two-part/balanced solution and both calcium and alkalinity do not seem to be keeping pace with maintaining a balanced state, simply increase the amount of each being added. If additional amounts of a balanced solution still fail to increase them, check the system's magnesium level as it may be too low. It should be at or near 1350 ppm at 1.025 specific gravity (NSW) or at a minimum, three times the calcium level.

As to a high alkalinity and low calcium level, if using a calcium reactor keep in mind its 'media' can wear out, i.e., its calcium content becomes depleted, which will happen far prior to its carbonate being used up. When this happens, if testing its effluent, you'll see calcium content drop and alkalinity rise/remain quite steady as previously see in earlier tests. (always good to keep records of 'all' tested water parameters!) I always recommend changing reactor media once yearly, even if the reactor cylinder still appears to have sufficient media!

Calcium Supplements vs. Aquarium Size/Complexity

After reading the above there may still be a question as to which path to go when it comes to maintaining the proper amount of calcium in one's reef aquarium. Of course it's more involved than just adding a calcium additive. One needs to keep in mind calcifying organisms, e.g., corals, clams and even coralline algae, need calcium 'and' carbonates (carbonates and bicarbonates/alkalinity) in the water at a favorable pH to do so! Therefore, the method used needs to provide 'both' without harshly impacting the pH.

Keep in mind these calcifying organisms extract calcium and carbonate from the water in equal proportions, i.e., 1 meq/l of alkalinity for every 20 mg/l of calcium used. Therefore methods of supplementation called 'balanced' methods should add these components in these amounts, such as what calcium hydroxide (Kalkwasser), calcium reactors, two-part calcium and alkalinity additives, and calcium acetate provide. However, before these measures are implemented the starting condition of the seawater must be assessed. If the water is not in a balanced condition, as noted above in this chapter, it could be the salt used is not in a balanced state to begin with, or the freshwater used for evaporation has an elevated calcium or carbonate level, or the system is low in magnesium (refer back to magnesium in Chapter 10).

If unbalanced, there are individual products that add calcium or magnesium and/or boost alkalinity, but as explained in the 'A Day At The Beach' discussion also in the previous chapter, they sometimes have a seesaw effect if not applied in a balanced fashion. Therefore its really necessary to know what level of calcium and alkalinity is being used daily in the aquarium 'prior' to making any additive additions!

To do this, stop all calcium/alkalinity additives and test these two items over a period of 5 days. This will tell you how many ppm of calcium the aquarium is using daily, e.g., a 100 gallon aquarium had a total drop in calcium of 50 ppm, or about 10 ppm per day (5.7 grams/5680 mg) over the five days. Keeping in mind calcium carbonate is 40% calcium, there is a need to supply 14.3 grams of calcium carbonate daily if using a calcium reactor or two-part additive, or 10.5 grams of calcium hydroxide/Kalkwasser to maintain a fairly steady calcium level. Yet keep in mind Kalkwasser can only supply a very small amount of calcium, e.g., about 1 gram per liter of a saturated Kalkwasser solution. Because of its extremely high pH, about 12, it would not be feasible to add 2.5 gallons of Kalkwasser to a 100 gallon aquarium per day unless carbon dioxide was in use or an acid additive such as vinegar was used to prevent pH spikes. Even then, (because of evaporation limits) it's a doubtful path to take!

For smaller systems with low calcium carbonate demands, a two-part solution is probably the easiest way to go along with small water changes. In larger more complex systems its cost would be prohibitive; therefore a calcium reactor is the best approach, possibly along with some Kalkwasser being used for evaporation makeup which will mitigate the introduced carbon dioxide from the reactor that tends to somewhat lower system pH. Possibly, if Kalkwasser use is not preferred, and pH runs somewhat low due to dissolved carbon dioxide in the calcium reactor effluent, a pH controller can be mounted in the reactor effluent or the aquarium bulk water and connected to a solenoid on the reactor carbon dioxide bottle that will shut off its flow when deemed necessary.

Once the system is within the balanced parameters as noted in the beginning of this chapter, retest again to assure the right levels of calcium and carbonates is being added daily to give one peace of mind! In fact test weekly even if parameters appear adequate because aquarium environments change as they age. And keep weekly records of all your tests, as they can show trends in different directions that can alert you to changes that may need more attention.

Seawater Summation

In closing, if I can leave you with one important aspect concerning these three chapters, it's the word 'Balance!' Take what is discussed here and try to maintain a balanced seawater environment. If experiencing something other than said condition test all important parameters, possibly twice, and if still unable to correct send those test results (and how the tests were made/brand kits used) along with a very good description of the aquarium's maintenance and bioload to me via this website's contact page and I'll do my best to help.


Lets now move to Section Four – 'System' Husbandry, and in Chapter 12 discuss Algae – the Good, Bad, and Ugly!