In 1989, Tunze was the first manufacturer to develop a CO2-controlled calcium reactor. A circulation pump is used to pass the water enriched with carbon dioxide through the hardness granulate. The carbon dioxide reacts with water to form carbonic acid which dissolves the calcium carbonate, discharging softened water from the reactor. The Calcium Automat 3171 is suitable for cabinet systems and aquariums up to 317 gallons.Useful Articles:Four Ways to Supplement Calcium and Alkalinity.