Coral Essentials, Part A Calcium is a concentrated source of liquid calcium, 200,000 ppm (mg/L). Calcium is an essential component in the formation of calcium carbonate skeletons, i.e. coral growth. The calcium levels in marine tanks need to be checked regularly to determine the take up in your system. How much calcium is being used can be calculated by testing at regular intervals to see how much the calcium level drops during the set interval. Then it is simple to calculate dosing requirements to suit the depletion rate. After you have determined this, a regular check of the calcium levels should be made. Your tank will change over time as coral grows, new pieces are added as well as invertebrates that also take up calcium. We have found ideal calcium levels to be at about 430-470ppm for most aquariums. Levels of 470+ ppm are desirable if you want to maintain high levels of growth in a SPS and hard coral dominant system.