Ok, so i have a Tom Aquatics doser pump, connected to my ATO. When the pump turns on, it takes water from the reservoir, thru the pump and into the "reactor". THe tubing goes into the top of the locking lid container, and all the way to the bottom, so when new water comes in it runs thru the kalk. The water then "overflows" thru the tubing running to the sump where it empties. Its really basic, only 2 tubes and a pump.