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.
Conclusion: 
In a healthy aquarium growth and multiplication of corals, desired calcareous algae and other organisms results in calcium depletion. Because of the importance of calcium timely corrective measures would have to be taken. For that purpose a proper calcium additive together with an accurate test kit are required.
Our calcium test is capable in resolving the calcium content in 10 mg/L steps. The color change is sharp and facilitates the detection of small but highly significant fluctuations in the calcium concentration. Salifert is the only one in offering a true accuracy and precision as claimed.
The kit can perform approx. 50 - 100 measurements.
Salifert's Coral Calcium additive is manufactured using a very special procedure. This results in a highly concentrated additive that not only makes calcium addition easy, it also avoids that the ionic balance is disturbed when used in combination with our KH + pH Buffer or any other sodium based buffer. Common additives, which contain only calcium chloride or improperly use of kalkwasser (calcium hydroxide), can upset the ionic balance resulting in aquarium water very different from NSW.