I also have a GEO Kalkstirrer. Not sure if its an older one or not? It has a black box bottom and pulls the kalk sediment directly through what looks like a PVC end cap with holes drilled in it. Looks a little different then the ones posted. I think its been modded as well, with a new pump.
I got it used about a month ago, and has never had any kind of issue at all. Great great great stirrer.
I dont use a pump at all actually, i have it hooked directly too my RO/DI thats connected to the spectrapure ATO. The pressure from my house pushes the water through the reactor.
I have a 1/4" valve half shut so the water doesnt come shooting out when the ATO first kicks on. I stir once a day, should i stir more?