There are a number of parameters you need to monitor to maintain a healthy and successful reef tank. Calcium is another essential element for coral health in a saltwater aquarium. Many corals, mollusks, and algae need calcium to make their exoskeletons and other structures. The corals get most of the calcium for this process from the surrounding water. Normal seawater has a calcium level of about 410 ppm (higher in the deep ocean) and most reef aquarists try to keep slightly higher than natural calcium levels. The ideal level is 425 ppm. It is also important to understand is that calcium levels are tied to pH in that they tend to counteract each other. Increasing calcium forces alkalinity to decrease and vice versa. Some aquarists with a very light demand may be able to maintain calcium with water changes. But some established aquarists with growing, hard corals and coralline algae will require some calcium supplementation. The supplementation depends on the demand. Talk with your Pisces Reef fish specialists to see what you are needing.