kalk reactor design

Ok so I know we went over this a few months ago but just a thought.
What if you didnt want to use the kalk reactor for your top off water but instead only wanted to use it when nessisary for controling/raising ph ?
Have one chamber with a float valve and a small pump hooked to a ph controler. Then build a conventional style reactor and put a ball valve or other type of restriction on the output. When the ph falls the reactor would dose at a slow controled rate. when it wasnt nessisary it would dose nothing.
Just a thought.