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Why don't you just feed the ro directly to your ato where your Kalk is at? Use your float for the ato/kalk tank. Or am I missing something?
I manually refill my ato/kalk tank as needed and that is then fed into my sump by a float switch (autotopoff dot com).
Manually filling anything is what me and BODI are trying to avoid. Plus many people don't have the space for a 33 gal brute much less have it sit in there living room, or their wife's jacuzzi, lol! It can be done properly but requires as BODI mentioned a dosing pump and timer. A float valve dripping kalkwasser? That is a sure way to see it fail with all the precipitation!