I have a constant rise in pH such that I'm having to put acid doses in the pool at least a couple times a week. I'm using a combination of pucks and liquid chlorine -- just enough pucks to keep things "leveled out" and to reduce the amount of times I have to add liquid Cl. The pH is a little bit worse in the summer, which makes sense since I add more liquid Cl, which adds to the rise in pH, but even now in the winter I'm still adding acid twice a week even though my liquid Cl additions are FAR less frequent. Given that the plaster is no longer "new" (two to three years old at this point) the only thing I can think of that would make the pH rise so fast is aeration.
I don't have any water features, but I see a constant fog of tiny bubbles coming out of my inlet jets, indicating that air is getting into the system somewhere. I had a leak detection guy come over an check for leaks by pressurizing everything, and after his tests he concluded that I did not have any leaks. I'm using a Kreepy Krauly for the cleaner, which somehow pulls in a little air as evidenced by a constant bubble in the leaf trap that comes back even if I remove it. At first I thought that it was just hose leaks causing the air in the line, but I put on new hose sections and it continued to happen. After thoroughly checking the hose, I started to wonder if the cavitation could cause air to appear in the line, which could then cause pH rise. I always thought that cavitation bubbles would instantly disappear (i.e. that cavitaiton couldn't cause air bubbles coming out the jets), but I'm not sure how everything works together in this situation. If cavitation could lead to pH rise, I wonder if the pump itself could be causing enough cavitation to explain the situation. It's a VERY old pump that had the impeller replaced by the previous owner, but I think it was done on-the-cheap, so it wouldn't surprise me if it could be causing problems.
My questions, therefore, are:
1) Does the fog of little bubbles indicate enough aeration to make the pH rise? In other words, how much aeration causes how much rise, and does the evidence I'm seeing indicate enough aeration to see such a noticeable rise in pH?
2) Could cavitation alone (either in the KK system, the pump or both) cause the air that I see coming out of the jets?
3) Could enough cavitation, by itself, cause pH rise, and could the pump do this?
4) Does the air in the leaf trap (in-line with the Kreepy Krauly hose) indicate a hose leak, or could cavitation explain this.
Are there any other questions that I should be asking here? I'd really like to figure the situation out after discovering that many people only have to add acid every few weeks or even months. Even people with salt water Cl generators don't seem to need as much acid as I do. I feel like there is a solution to this -- I just haven't been able to find it yet.
Thanks for any help with this,
approx. 21K gallons
CC negligible (.5 or less)
pH (target) 7.4 - 7.5