a small MJ would work but you'll have to reduce the pump output to fit the reactor....I use one of these Tom Aquatics Aqua-Lifter Dosing Pump it pumps water from my ATO container to the kalk reactor and gravity feeds from the reactor to the sump,the K2 uses an RO/DI tube to feed it with and the RO/DI tube is a perfect fit to the Aqua-Lifter pump,I also added a ball valve to the output side of the pump to control the flow,plus the pump is plugged into a timer so that it only doses at night time