Precision Marine there are two ways Calcium can be added to your reef tank, the Calcium Reactor or the Kalkreactor pictured here. You can either gravity feed through the Kalkreactor from a freshwater top-off system to your reservoir, or use a dosing pump.Precision Marine choses a reliable water pump in lieu of the magnetic stir bar, which tends to jam, bind and wear the acrylic.This model also includes a threaded opening at the top to enable adding Kalk powder without removing the lid.Master fabricated and computer cut, the KR620 is a very nice piece of equipment.