The Calciumreactor 400 is a completely sealed system. It is operated at a very low flow rate. Within the reactor calcium and calcium bicarbonate ions are release by the controlled dosing of CO2 gas. This provides the calcium hydrocarbonate that hard coral require to build their exoskeletons. The filter can be installed in almost any position, inside or outside the aquarium or the cabinet. For the water flow, we recommend the Dosing pump SP 3000. The reactor is filled with Hydrocarbonate - a pure form of calcium carbonate with an extremely low phosphate level. For optimum control and the most economic use of the CO2 gas, we recommend the reactor be used in conjunction with an Aqua Medic pH controller. The reactor is already equipped to accept our pressurised electrode. Dimensions (without electrode) : 14.4 x 10 x 37 cm c. 5.8"x 4" x 14.5" ( L x W x H) Assessories: pressure proof pH probe with screw connection PG13.5, short CO2 complet, for CO2 supply. Hydrocarbonate as refill Dosing pump SP 3000