Corals consume calcium at a relatively rapid pace. Hence, it is necessary to replenish calcium on a regular basis so as to maintain levels equivelant to natural seawater. Aslo, alkalinity will soon be depleted by growning organisms. In view of it, a calcium reactor is a simple and convenient solution used to maintain calcium level and alkalinity in a reef aquarium. They ask for little maintenance after the initial setup and are almost a necessity for tanks where stony corals is heavily kept. They have a high demand for calcium and alkalinity.