Calcium Chloride is a very pure anhydrous grade free of phosphates and nitrates. The advantage of using Calcium Chloride as a calcium supplement in marine aquaria is its very high solubility in water. This property allows the aquarist to rapidly adjust calcium concentrations to desired levels. The aquarist should be aware that Calcium Chloride does not add bicarbonate and carbonate ions to the system. Since most calcifying organisms require these ions in addition to calcium ions, the aquarist should monitor the alkalinity frequently when using Calcium Chloride and make the proper adjustments with a buffer additive. Calcium Chloride can directly reduce alkalinity by elevating the calcium ion concentration to excessively high levels and thereby initiate the precipitation of calcium carbonate from the water. This may or may not be visibly detectable, depending on the magnitude of precipitation. Excessive use of Calcium Chloride may disrupt the balance of ions in a marine system by the continued addition of chloride ions. Since saltwater contains such a large concentration of chloride ions, it would take a very long time before significant chloride imbalance would occur, especially if water changes are performed. We recommend Calcium Hydroxide as a better long-term calcium supplement, but Calcium Chloride can be very useful in restoring proper calcium ion levels should they drop while using Calcium Hydroxide. 1 teaspoon will raise the calcium level by about 50 ppm in 10 gallons of water.