The Aqua Medic Calcium Reactor is a module for the creation of a natural calcium carbonic acid equilibrium in the aquarium. It is filled with hydrocarbonate. As calcium carbonate is not soluble at pH values, that are recommended in seawater aquaria, CO2 has to be injected into the reactor. This results in a local decrease of the pH and the solution of Calcium hydrogen carbonate. This way of calcium dosing does not effect the pH, like the use of "Kalkwasser".

Like the smaller calcium reactor, the calcium reactor 5000 is a closed system, designed for universal use. It is supplied with an internal circulation and a connection port for a pH probe with standard thread. The reactor has a volume of 30 l and comes with a bag of Hydro-carbonate (50 kg, 110 lbs). The flow rate through the reactor shall be adjusted depending on the Calcium demand of the aquarium, to 12 - 30 Liter /hr (3 - 8 gph).