This gets a lttle tricky,,,,,, R/O to holding tank metered by the "valve", run an output line from the holding tank to a dosing pump input controlled by a "float switch" in your tank or sump, then take the output side of the doser and go directly into the input of the reactor, take the output of the reactor and go directly into the tank or sump. Basicly youre incorporating a holding tank into the top off system instead of going directly to your sump. This allows you to add kalk in direct proportion to evaporation. Confused yet?
R/O >>> holding tank >>> doser >>> reactor >>> tank or sump