The Hydor Performer CR 750 Calcium Reactor was designed as a powerful and user-friendly calcium supplementation unit. It supplies biologically available calcium to your aquarium to promote and maintain healthy coral growth. It features an easy-fill design for convenient media application, a precision bubble counter to monitor CO2 levels, and can be connected to the majority of CO2 systems. This reactor has a 1.5 gallon media capacity and is rated for aquariums up to 200 gallons in size.