I think his problem is that there is so much kalk in the reactor the stirring mechanism cannot stir... But its not clear to me from his post.Too little kalk and it does not form a cloud at the bottom/not mixing. I know how the typical sludge at the bottom of a reactor is and had never posed a problem with normal kalk.
The way a TLF reactor works in not by a constant drip and stir once in a while. Water is pumped into the reactor and down a tube near the bottom and on the bottom of the tube is a device that spins when water is pumped through it mixing the kalk. The excess water that is pumped in overflows at the top of the reactor and into the tank. Mine is set up to run every 25 minutes so it's not as though the a great deal of time has lapsed between stirs to allow the kalk to turn to paste.