If calcium chloride, CaCl₂, is used as the source of calcium to a reef aquarium then the following can be used to make a DIY stock solution. It can also be added as a dry solid, but it has to be pre-mixed before addition to the aquarium and can be harder to measure out. The use of a stock solution gets around both of these problems.

The variables used to make the calculations are as follows:
M₀ = Mass of calcium chloride required to make the stock solution (grams)
V₀ = Volume of stock solution (litre)
C₀ = Calcium concentration of the stock solution (ppm)
V₁ = Volume of stock solution dose to give calcium concentration rise of C2 (cm3)
V₂ = System volume (litre)
C₂ = Calcium concentration rise required in the system (ppm)
Ca = Fraction of the type of calcium chloride that is calcium by weight: 0.3611(CaCl₂), 0.3107(CaCl₂.H₂O), 0.1829(CaCl₂.6H₂O)

The value of Ca depends on the type of calcium chloride that is used to make up the stock solution. In most cases this will be CaCl₂, the dehydrated form, so the valve for Ca in this case is 0.3611.

The concentration of the stock solution, C₀, is really arbritary, but the higher the concentration the less of the stock solution has to be added to give a certain system concentration increase. Although the higher the concentration the easier it would be to overdose and cause problems. A good number to start with is around C₀ = 50,000ppm, which is the concentration of some commercially available calcium chloride additives. The mass (M₀) of calcium chloride required to add to the stock solution of volume V₀, to give concentration C₀ is given by:

Therefore to get C₀ = 50,000ppm stock solution, using CaCl₂, M₀ = 138 grams is required to be added to V₀ = 1 litre.

The equation to determine the volume (V₁, cm³) of the stock solution (concentration C₀ ppm) required to increase the system (volume V₂, litre) calcium concentration by C₂ ppm is as follows:

Therefore to increase the system of V₂ = 100 litre calcium concentration by C₂ = 100ppm, using a stock solution of concentration C₀ = 50,000ppm need to added V₁ = 200 cm³.

As another calculation example, so that it is easy to see how it works, lets say that a 5 litre dosing solution is to be made up with a concentration of 60,000ppm. That would require 966 grams of CaCl₂.H₂O. Then to add this to a 150 litre system to increase the calcium concentration by 50ppm, 125 cm³ of the stock solution is required.

Calcium chloride has a very high solubility, with it being possible to pack up to over 1,000,000ppm into water, which is a highly potent solution. Take great care when making up these solutions and adding it to a reef aquarium. It would be very easy to over dose if great care is not taken. Always err on the side of caution, all that will have to be done is to add a little bit more at a later time. This is much better than putting in too much, it cannot be taken out again without having to do a major water change and sustaining some damage to the inhabitants.

Disclaimer: OZ REEF is not responsible for anything that occurs to yourself or your reef aquarium if you use such a solution made using the above information. Take care while using these solutions and compounds.

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