The ratio of alkalinity to calcium that should be added a reef aquarium is based on the ratio at which it is used up. If this isn't the case, then over time major ionic balances can occur, causing problems.

The formation of calcium carabonate, CaCO₃, requires 1 meq/l alkalinity to 20 ppm calcium.

Therefore, the technique used to add calcium and alkalinity should done so at this ratio. Calcium carbonate reactors and calcium hydroxide dosing does this automatically. If separate calcium and alkalinity additives are used, care must be taken to ensure that they are added in the correct ratio.

An interesting fact is that there is actually an over abundance of calcium ions relative to the amount of alkalinity present in natural saltwater. This is demonstrated by taking the upper limit of the recommended range of alkalinity of 4 meq/l and calcium of 450 ppm. If all of the alkalinity is used up, falling from 4 to 0 meq/l, to form calcium carbonate then that will only use up 80 ppm calcium of the 450 ppm available, dropping the concentration to 370 ppm. This is the reason why calcium levels are seen to be more stable than alkalinity.

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