I'd agree about the mess - won't work as drawn
aside from hooking your float valve up to that kalk
reactor, how about hooking it up to your ro
unit instead ... having a nice constant water supply is always good.
put it in with your sump and skimmer so the ro
water gets to mix with saltwater a bit before it gets into your refuge
if you want to stick with the 2 sump design, have the higher tank drilled and a stand pipe installed to the water level you want to keep, then it will automatically drain into your refuge and get returned to your main tank.