The water in St. Louis County, Missouri ranges from 9.7 to 10 according to the water company, and it measures off the scale with my basic Taylor test kit. When I opened our pool just after Memorial Day, I found out that our heater was shot (bad sensors; repair cost too high and repair temporary). After doing some research, I had it replaced with a Raypak (lost most, if not all, of June).
My Ph tested high, but I didn't do anything but test it for about a month. Then I tried some powder Ph down; it barely moved. I tried again about a week later, with the same results. A few days after that, I picked up some acid and added that. I got a low reading just above 7; so I figured I was fine; the next top off of water would raise it right up.
About a week later my heater quit. The service company came out and said the heat exchanger was shot due to low Ph. The tech said it measured 6.1. I was also told that my total alkalinity was too low at 60 (I figured I was fine, since Poolmath recommended 60 to 80)
The heat exchanger has been replaced. I raised the total alkalinity to 70. My Ph is still testing high (I bought a new test kit and some strips; they all test consistently, and the tech verified my technique was fine). At the tech's suggestion, I have been lowering the Ph very slowly by putting in half the amount of acid that Poolmath recommends to go from 8.2 to 7.5 (and I measure higher than 8.2). I've done this three times without getting my pool below 8.2 let alone 7.5 to 7.8 where I want it.
I don't want to ruin another heat exchanger. I'm not doing anything appreciably different than I have before, and I've never lost a heat exchanger. Because my season was greatly curtailed, I have not added any cyanuric acid; I've just monitored chlorine and kept it in range with bleach as needed and leaving my SWCG on high. Any thoughts?