Maintaining Calcium Levels

What affects them? How do you ensure that enough is available?

Calcium levels in an aquarium fluctuate. They do so for several reasons:

• How much calcium is added
  • Either in the form of limewater (kalkwasser)
  • or in the form of some other calcium containing additive
    • Calcium chloride
    • Calcium chloride mixed with other calcium containing products
    • Calcium alginate
    • Calcium gluconate
    • sometimes even other forms
• How large the calcium demand in the tank is:
  • uptake by animals (the more calcium requiring corals, the faster the concentration will be lowered and the more frequently you will have to add it or the stronger the solution will need to be
  • uptake by the system itself. Some calcium may be uptaken by rock (cementing rocks together)
  • loss due to precipitation as a result of interaction with acids in the tank's water
  • loss due to formation of calcium carbonate
    • in the tank
    • in the reservoir from which you dispense (if one is used)
• How strong the calcium additive is:
  • this can be the calcium added as kalkwasser. Strong in this case means saturated. Such KW has a pH of over 12
  • or the calcium added in some other form: how much calcium is in the compound you use and how much of it is bioavailable
  • Is the calcium in its inorganic form?
  • is it organic?
  • is it chelated?
• Does the system loose calcium in any other form
  • precipitation on heaters
  • loss through the skimmer
  • loss of calcium in conjunction with salt creep (salt and calcium combined)
• Is calcium added to the water from some other source
  • rocks
  • sand, for example oolitic sand or coral sand:
  • crushed coral
  • crushed shells
  • aragonite present in the tank
  • other forms of limestone that slowly dissolves
• Uptake by animals other than corals or by other life forms:
  • coralline algae (the red, purple and pink types that grow on rock etc.)
  • calcareous algae: algae such as _Penicillus_ and others
  • shell building animals (mostly crustaceans). These can increase the calcium demand a great deal. Clams, especially the _Tridacnid_ variety can really put a heavy calcium demand on the water. Note that tube worms with a hard tube also remove calcium.

As you can see, the calcium level can be affected by many causes and can be influenced by many factors, some that you may not always consider.

Note also that it is important when measuring your calcium levels to understand what your test is actually measuring:

• Calcium carbonate
  • in which case the number you come up with will need to be adjusted in some way to reflect the actual calcium level versus the calcium carbonate level for instance
• Actual calcium.
  • in which case no adjustment to the number is necessary.

Let's look at this more in detail

Adding Limewater

Limewater is simply a mixture of calcium hydroxide and water. What is important when preparing limewater is to make sure that:

• the solution is saturated
  • use 2.5 to 3.0 tsps per gallon of water you prepare
  • stir gently to mix the compound and water but without introducing too much air and carbon dioxide as this results in the formation of calcium carbonate. When this happens your KW is weaker than it should be. The pH of saturated KW is over 12.0
• the water used is pure and does not contain pollutants such as:
  • nitrates
  • phosphates (simple and complex ones, inorganic and organic ones)
  • silicates and silicic acid (e.g. sodium silicate added by water companies to purify the water)
  • organic material (breakdown of protein or living organisms)
  • heavy metals (too much iron, copper etc.)
  • organic fertilizers and pesticide residue (especially the case in agricultural areas)

• a real high grade quality calcium hydroxide powder. Buy from a reputable manufacturer and do not skimp on the price here as you may be getting low purity calcium hydroxide if you do. This will introduce impurities into the water. If you do so you will have to spend money later to remove them. Avoid this by buying high quality product.
• treat the water you will be adding to the powdered calcium hydroxide real well so it is as pure as you can get it. Pre-treating the water makes a lot of sense. Not only is it easier to remove unwanted compounds from fresh than from saltwater, but if you do not remove it now, you will spend even more money later to remove these compounds from the aquarium.

You can go to our web site and in the saltwater library under water quality articles you will find a free article that explains how you can do so. The procedure is not complicated and does not require a great deal of equipment. It is well worth doing so, to save you time, trouble and money afterwards. Indeed if you do not remove it now you will need to remove it from the aquarium water itself later. Remember that it is always more difficult to remove just about anything from saltwater than it is from freshwater.

Even after you use an RO or DI unit, and believe your water is reallly pure, you may wish to test it for some of the pollutants mentioned. RO units remove on a percentage basis. DI units remove what the resins contained in them have an affinity for but only for as long as the resins can absorb more of those compounds. They get saturated and need to be regenerated using special chemicals. The higher the amount of pollutants in your water the more frequently you will need to regenerate. The same applies to RO units: the higher the amount of pollutants the more will of them will be left after the water has passed through them.

Let me explain the RO principle: a membrane inside the RO unit remove pollutants but, does so on a percentage basis. The better units remove around 96 % of all pollutants. Let us take an example:

• your raw (e.g. tap) water contains 10 ppm of PO4
• the unit removes 96 percent
• 96 % of 10 is 9.6 ppm
• this leaves 0.4 ppm of PO4 in the effluent water (the water that comes out of the RO unit)
• 0.4 ppm is about 10 to 11 times higher than what your PO4 levels should be.
• not being aware of this could lead you to believe that because you are using RO water, it is pure
• I have just proven to you that it is, in fact, not.

As you can see from the above illustration, even after water goes through an RO unit, it can still contain far too many unwanted nutrients.

The same applies with DI units. Indeed, the resins remove nutrients and pollutants and then load themselves with them. When they are saturated they no longer remove these pollutants. The result is that they pass right through the DI unit and end up in the aquarium.

The only way to know whether the water you obtain from these two filtering methods is actually suited for your tank is to test it on a regular basis.

The reason that this is important has to do with several issue relating to the aquarium and with calcium levels in particular.

Some of these issues are:

• high nitrates are detrimental to all animals especially if high levels are maintained for long periods of time.
  • the library of our web page contains an article on nitrate, in fact it contains several on that topic. You may wish to read them (articles refer either to nitrates directly or to algae).
  • nitrates were not viewed as harmful for the longest of times but empirical evidence demonstrates that they affect the fish and can affect the corals negatively and should be kept a low levels. Details can be found in the articles just referred to.
• phosphate are undesirable because:
  • they bind with calcium and form calcium phosphate which corals and other animals cannot absorb or uptake. Their levels should, therefore, be kept low. Indeed when they are high, it may become difficult to raise calcium levels to the desirable concentrations.
  • phosphate soon gives rise to the appearance and proliferation of undesirable algae in addition to what was just mentioned: it inhibits availability of calcium.
• silicate is undesirable because:
  • it promotes the growth of brown algae of various forms
    • filamentous
    • patchy
    • bushy
    • encrusting
  • out of the above list all forms are detrimental but the ones that affect corals the most are the encrusting ones which can interfere with calcium uptake but can also grow on the coral's skeleton and with their upward growth push the polyp loose and get it to detach from the skeleton.

Keep an eye on the nutrient concentrations as this is important with respect to how much "calcium" will actually be "available" to all animals that require it.

I indicated earlier that to make kalkwasser (limewater), it is good practice to use 2.5 to 3 teaspoons of calcium hydroxide per gallon of KW you prepare. When you do so and stir the mixture, the resulting solution will be saturated. This means that the water will have absorbed as much calcium hydroxide as it can. Note that colder water absorbs more of it than warmer water. If you were to measure the pH, it would be over 12.0

Now that you have your limewater ready, you can start using it to raise the calcium levels in the aquarium. This is done by replacing all water that evaporates from the tank with this limewater and monitoring how the calcium levels behave.

Be aware that the mere fact of replacing all the water that evaporates does not necesarily ensure that your calcium levels will be high enough (generally suggested concentrations range from 450-480 ppm on a constant basis).

Indeed, and to give just one example, in an aquarium with low evaporation and a high calcium demand (see earlier in this document), the amound of limewater you add may not be able to ensure that your Ca++ levels are high enough. This is not an unusual situation in a tank that is heavily loaded, even if the evaporation is relatively high. Only testing will determine whether your calcium levels are in the right range. Test regularly to ensure that you know what the calcium demand is, so you can add to the tank what is removed on a continuous basis.

To determine how much calcium a tank requires (or how much is depleted) is easy to determine and is calculated for a 24 hour time period in this document. You could use any amount of time, you do not have to use the one suggested here.

Test your water for calcium content on a given day and write down the time you took the water. Test and write down the result. Do not add any KW or any other form of calcium to the tank. Wait exactly 24 hours and retest the water. Write down the result.

The difference between the result from the first test and the result from the second one, is the calcium demand for your tank for a 24 hour period. Note that you need to remember that this is the calcium demand based on the load you have in the tank at that time and that if you add more corals the demand will increase of course. Note also that the demand increases even if you add calcareous algae and even when the coralline algae start to rapidly expand in the tank.

Calcium demand is never a stable number. It varies and will usually increase over time as you add animals and as more coralline algae appear in the tank.

This should be an indication that you need to check your calcium levels regularly as even though you may know how much calcium the tank requires and may have determined how much KW you need to add daily to provide that amount, when the demand changes you will need to add more limewater to remain at the calcium concentration level you are trying to keep your tank at.

Update 3, Feb 13, 1997 Should you have any questions feel free to Email Me