Hi Yanek
I have my Geo's reef Kalk reactor hooked up to my RO/DI reservoir which is controlled by 2 Reeffanatic float switches, and to prevent accidental jamming/malfunction of the float switch it's on a timer which allows 10 mins of top-off a couple of times a day then shuts off.
So far coming up on 1 year with this setup, no problems in over dosing Kalk, the only trouble i did have was a faulty check valve which allowed kalk water to siphon back into my reservoir and gave me an instant snow storm when i mixed a batch for a water change.
As for which brand to recommend, i've only ever used this one and had no problems, it has a MJ as a mixing pump on a timer that stirs 4 times a day for 10 mins, i don't think kalkreactors have to as fancy as skimmers or Ca reactors, having said that i love my Deltec PF501 Ca reactor.
HTH
Anton
At work, unable to stuff my face with turkey