Calcium alone is not sufficient to form the skeleton of corals and calcareous algae. This also requires carbonate and bicarbonate. These two substances also have a great influence on the stabilization of the pH in the correct range for 8.1-8.4. Such stabilization is also called buffering.
The total concentration of carbonate and bicarbonate is an abbreviation for carbonate hardness, alkalinity or carbonate.
Natural seawater has an alkalinity of about 2.7 meg / L or about 7.5 dKH as expressed as carbonate hardness.
For a stable system, the alkalinity or carbonate hardness must have a value comparable to natural seawater or slightly higher. Preferably between 7 and 10 dKH.
Since the major buffer components used for coral and calcareous algae growth are bicarbonate and carbonate, these must be added / corrected when the alkalinity decreases.
The alkalinity or carbonate hardness should be kept as stable as possible. The Salifert test is extremely suitable for this.
The Salifert KH / Alk test is very simple. It measures in sufficiently small increments of 0.1 meg / L or 0.3 dKH with a sharp color change.
With this test kit you can perform approx. 100-200 measurements.