Calcium Supplement for All Marine Fish & Reef Aquaria Overview High-purity powdered calcium. Increases the concentration of calcium in marine aquarium water to provide corals and other reef-building invertebrates with one of the most important elements required for growth. Stronger and more economical than liquid calcium solutions; created for hobbyists maintaining multiple reef aquaria. Formulated by a marine scientist. It is recommended that the calcium concentration in the aquarium be determined by using an accurate test kit prior to supplementing. Do not add this product directly to an aquarium containing live animals without first diluting in water as directed.