Seachem Reef Kalkwasser is a pure calcium hydroxide with unsurpassed purity and solubility characteristics. This calcium hydroxide meets or exceeds the purity of competing brands designated for reef use. Calcium hydroxide is used to prepare limewater (kalkwasser) solutions that are used in an automated dosing system that replaces evaporated water. Kalkwasser solutions maintain calcium directly and carbonate alkalinity indirectly. However, its capacity to perform these functions is dependent on evaporation rate and CO2 concentration. If these two factors are insufficient you can provide additional calcium with Reef Advantage Calcium, Reef Complete, or Reef Calcium, and carbonate alkalinity with Reef Builder or Reef Carbonate (do not mix these directly with a kalkwasser solution). Reef Kalkwasser can also precipitate phosphates and impurities from the makeup water while maintaining a high pH which is important for proper calcification rates and for oxidizing various organics in reef aquaria. 500 g makes 650 L (166 gallons) of kalkwasser solution.