OK, I ordered a non-return valve (aka check valve) that will be inline between ATO container and Kalk reactor..
So when peristaltic pump pumps Kalk water into mixing chamber and the tank in this very moment does not need RO water top-off, the water will be pushed back from mixing chamber into Kalk reactor..
So when peristaltic pump pumps Kalk water into mixing chamber and the tank in this very moment does not need RO water top-off, the water will be pushed back from mixing chamber into Kalk reactor..