My pool is fiberglass (which I assume is non reactive) and I live in Florida so the pool is open year round. I do turn the output on my SWG down in the colder weather and shorthen the pump run time a few hours but I still had the pH rise. My alk stays pretty constant....might be from my fill water which has a TA of about 110 ppm. The only alkaline substance that goes into my pool on a regular basis is the sodium hypochlorite produced by the SWG.