I made a simple Kalk Reactor out of a Fluidized Bed Filter (basically a Phosban style reactor) I had laying around, it runs off of a Aqualifter pump that feeds from my ATO reservior. I added a check valve between the the Aqualifter and the reactor to keep it from backflushing through the pump and into the ATO reservoir. By doing this only RO water is never in contact with the pump which should cut down the need for cleaning any build up that would occur from the Kalk, and no Kalk gets back to my ATO res. so I don't have to worry about the corrosiveness of the Kalk laden water damaging my aTO pump.
The Kalk powder settles to the bottom of the reactor and the slow flow through it has been enough to keep it at saturation as the RO water has to pass through the slurry at the bottom of the reactor. It is also slow enough to keep only "clear" water from dosing into the sump. I do give the reactor a shake once a week to stir it up a bit.
I run mine through an AC Jr. and have it set to 10 minutes on out of each hour with a drip rate of one and a half drops per second. I also set the controller to shut it off at 8.3 pH. for safety. The normal ATO pump still keeps my water level adjusted, but runs much lless frequently now.
I feel by doing it this way, my dosing is much more consistant than just using the Kalk as strictly my top off supply.