High performance, quality calcium reactors incorporating a number of great features: Unique water intake system using a single integral pump which acts as both a supply and recirculation pump. This allows the V2 React Calcium Reactor to be easily installed in any aquarium set-up without the need for a second pump or any modifications to existing pipework. Integral bubble counter which enables easy, measurable dosing of CO2 to the Calcium Reactor. pH probe holder which accepts all standard sizes of pH probes and enables the Calcium Reactor to be used in conjunction with pH monitors or controllers for more advanced aquarium set-ups. CO2 pressure regulator which allows for the precise control, adjustment and dosage of CO2 to the V2React Calcium Reactor. Ideally used with TMC Coarse Coral Gravel (not supplied) but can also be used with other similar types of filter media. For aquariums up to 600 litres/120 UK gallons. Requires 3 litres/2.5kg of media