The fast and easy way to test your aquarium water for the right amount of calcium to encourage healthy coral growth. Ca is needed to help form the strong exoskeletons of your coral. 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.