Calcium is a major constituent of calcareous algae, skeletal material of hard corals and the skeletal needles of soft/leather corals. Calcium also fulfills many biological functions.
Quite often a too low calcium concentration retards coral and calcareous algae growth. NSW contains 400 — 450 mg/L calcium.
Which is also the value we should strive for. For a stable aquarium environment, the fluctuation in calcium content should preferably not more than approx. 15 mg/L. This automatically means that the calcium test should be able to monitor comparable fluctuations.