Auto top-off improvement question

[Guillaume]

My auto top-off is composed of an Apex controller dosing kalk by a little pump from a 7 gallons plastic box depending if the float in the sump and th Ph probe allow it.

I would like to avoid stirring 6 gal of kalk and transporting it from my RODI to the tank each week. Note that there is no space for the RODI near the tank.

My idea is to plug the RODI on a J. Sprung kalk reactor, then in the sump. But one part is missing and I don't know what to buy. That should be a sort of electric valve that would receive the RODI feed (typical ice machine tube), be controlled by the Apex and have its output on the kalk reactor.

Any equipment to suggest?

Thanks!