So what does it mean when you still see a significant pH rise in winter when the water is generally pretty cold (40's to 50's)? My pH still rises by 0.4 every week even though it's as cold as it ever gets in my area right now (Los Angeles area.) I let it rise to 7.8, then I knock it back down to 7.4, and I have to do this around once a week. The rise gets a bit faster in the summer when the water is warmer, but not "that" much faster. The plaster is a few years old now, so I don't see how that could be a factor, and I don't have any water features. I do have some aeration as evidenced by a light fog of tiny bubbles at some of the jets (I believe that the Kreepy Krauly is pulling in some air along the hose sections), which I posted about in another thread, but I'm still not clear if this could explain the rise.