Alkalinity and Calcium

Alkalinity and Calcium Content : Relationships and Constraints

© A. Thiel -1996, 1997 - Updated Feb 97 for the NetClub

From a chemical standpoint there exists an incompatibility between high dKH (alkalinity or buffer) levels and high calcium (Ca++) levels. Both cannot chemically co-exist. Whenever the dKH or alkalinity starts to rise, the calcium concentration will either go down or, you will have a very difficult time raising your calcium levels to the concentrations you want in your reef tank for good coral health and propagation (around 450 ppm according to what most authors suggest).

If you really wanted to test this, you could take plain saltwater, measure its calcium content and then start adding buffering compounds. As you add more of these and retest for the calcium content, you will notice that the latter becomes lower and lower.

At the limit, with dKH levels that are really high, adding Limewater to raise the calcium may even result in a calcium carbonate fall-out (white powder settling on the rocks and anywhere else in the aquarium). This white powder is not available to the corals because calcium carbonate is only marginally soluble in water. It does not contribute to the calcium concentration of your tank at all.

In the worst case scenario a total calcium fall-out occurs and the entire tank, including the glass or acrylic panes, become coated with a micronic thick layer of calcium carbonate that can only be removed with razor blades or, by emptying the tank and adding acidified water to it. Note that if a calcium fall out occurs, this micronic coating is present everywhere, including in your pipes, hose, skimmer and so on. Having experienced it, by provoquing it on purpose, I do not wish it to happen to anybody.

The time it took to clean the aquarium and all the hoses was just so long that you really want to do everything to avoid it happening to you. In addition, the stress created on the animals is sure to lead to problems. As already pointed out, and not once but several times, stress needs to be avoided at all cost.

Re-establishing the correct water chemistry needed is then one of the next difficult steps you will have to go through and that is not an "pleasant" or "short" experience at all. Doing so requires a lot of time and a lot of testing and more testing until you have it all right again.

But back to the main topic: If you wish to raise your calcium levels you should not add buffers (and certainly not chelated buffers) to your aquarium. You should also make sure that your dKH is in line with what is generally recommended. If it is too high, you will need to lower it first. Remember this well. Do not attempt to raise the calcium levels unless your dKH (buffer) is in the correct range.

With a dkH of around 7 to 8, you will be able to maintain high calcium levels without any problems. This can be done by adding Kalkwasser (Limewater), or Pure Calcium (a mixture of several soluble calcium compounds that are available to the animals that require calcium).

Remember too that there are several manners in which to measure the buffer: dKH, ppm, milliequivalents (and others still that we do not need to discuss here).

There is a definite relationship between all three since they express the same water quality standard. This relationship is as follows:

Once you know the buffer value in one of these measurements, you can easily convert to one of the other ones if you need to do so, or wish to do so. For instance: if the buffer strength you measure = 3 meq/l (milliequivalents per liter), this would correspond to 3 times 2.8 or 8.4 dKH and it would also equal 150 ppm. If what you measures was 165 ppm, the dKH would be 165 divided by 50 times 2.8 or 9.24 dKH. You can perform the calculations based on what you determine your tank's buffer value is if you wish. Most hobbyists nowadays measure in either meq/l or dKH (the German measurement manner often found in books on reef tanks).

Another situation altogether can occur: If due to a low dKH your pH starts going down, or fall rapidly, there are two ways to go:

All these method will result in an increase in the pH.

Both methods require that the additions be done very slowly. If you overdo it the pH will rise too fast and create stress for all animals. You must avoid this at all cost as stress often leads to parasitic infestations and possibly other diseases. I have outlined this in my books over and over again.

The less stress we create that our animals have to cope with, the less the chances are that the tank will become a problematic one.

If you use the sodium carbonate addition method, you need to use very high purity sodium carbonate not varieties that contain a lot of impurities. Thiel Aqua Tech sells a very high purity Sodium Carbonate powder to allow you to raise the pH slowly but surely, and not encounter any difficulties with impurities because it is so pure. The amounts added are very small and are added on a regular basis (usually several times a day). The same applies to our borate supplement.

Before resorting to these methods though, you should try to establish a proper pH with the addition of Kalkwasser (clear or milky). Other articles in this section deal with how to do so correctly. Our Main Article Library contains such articles as well albeit not in as much detail.

If your dKH is presently too high (e.g. 12 or an even higher dKH) you can safely reduce it by performing water changes with water that has a lower dKH. Stop using all buffering products you have. Do not use chelated buffering products at all and at any time. You can also reduce it by adding carbonated water in small amounts to the tank several times a day. By small I mean a few ounces at a time.

Do not add quarts or half gallons of carbonated water at a time; if you do you will create a great deal of stress for all animals in the tank (this includes fish and invertebrates and anything else present in the aquarium). When you use this method, test the dKH about 30 minutes after adding the carbonated water to determine its effect on the dKH. Based on that effect determine whether you need to continue adding it.

The longer you add carbonated water, the smaller you should make the dose you actually add each time. Indeed as the dKH gets lower, the impact of a given amount becomes stronger, hence the recommendation to lower the amount you add. Eventually your dKH will be where you want it.

Note that the first couple of additions of carbonated water (sometimes referred to as selzer water) may not have a great deal of effect on the dKH of your aquarium. This is perfectly normal. All you need to do is to continue adding more carbonated water as indicated above, following the manner described in which to do so. There is a free article in the SW library of our web site http://www.athiel.com, under the Water Quality Section that details the addition of selzer water in great detail. The Main SW Library.

There are other ways to lower the dKH, e.g. CO2 injection with a pH controller. This is certainly a viable way but, a much more costly one. You need to evaluate whether you really want to spend the kind of money it takes to set such a system up (Count on several hundred dollars to get good equipment). I personally believe that most hobbyists can use the method described here, and do not need a fancy CO2 and pH controller setup.

Others have attempted to achieve the same result by using diluted muriatic acid. While this will accomplish the same results, playing around with muriatic acid is dangerous. Having it around, especially if you have children, is dangerous too. It is also very easy to add to much of it to the tank and create a real sudden dKH and pH change, with the ensuing stress. I do not recommend this method unless you are totally comfortable with using this type of chemical.

There many come a time, too, where the dKH is too low (e.g. 4 or 5 dKH) and buffers need to be used to adjust it upwards. If such is the case, use only non-chelated buffering compounds. The reason for this recommendation is that we do not really know, at the present time, what chelators (e.g. EDTA, NTA and other phosphate based chelators do to the tank's water chemistry). Until we know more about this, I feel that it is better to be safe than sorrow.

As I just indicated, many chelators (especially the lesser expensive ones, which are often used because they are cheaper) contain phosphates, sometime plenty of them. This is the last compound we want to add to our aquariums. As you already know, phosphate levels should be kept as low as possible. If we do not, green algae of many types will start to appear in the aquarium.

The safe phosphate concentration that I recommend is 0.03 ppm as a maximum (note that this is less than 1/3 of 1 part per million). Most tests do not even measure that low. There is one that does: the Hach one (Model PO-19). It measures in 0.02 ppm increments, which is exactly what we want and need. You can reach Hach at 800 227 4224. They sell directly to the public.

I have tried to make this article as comprehensive as possible. You may have special situations in your tank that are not covered. Since you have paid for the article, you are welcome to send me email and ask whatever questions this article does not resolve. Questions on dKH


Updated Feb 27, 1997 by Albert Thiel for the NetClub ®