This two-part calcium and alkalinity maintenance system adjusts calcium, magnesium, and strontium ions to Natural Seawater ratios, and achieves a balanced ionic residual. Makes replenishment of calcium and alkalinity easy, and keeps your calcium and alkalinity in perfect harmony, assuring the optimum conditions for growing stony corals and coralline algae. Packaged in two 500ml (16 oz) bottles or as a concentrate in two 3785ml (1 gal.) bottles.