Richard,

I've been lurking(mostly) here for several years. You and many others have helped this new owner of a 25 yr. old IG plaster pool tremendously.

My pH has always tended to stay at the upper limit of the standard test kit. I usually let it run about 8.0, and don't do anything until it is clearly above 8.2. From memory (because my test results are at home, my TA is about 100-120. I have put about 40 lbs of borax in the pool (30,000 gal.)

This year, though, I have needed much more acid than before to keep it down. I think I'm starting my 7th gallon since opening in early April--more than I usually use in the whole season.

Rain isn't the problem here--East Tennessee is in the middle of the worst drought in 120 years. My refill water, from a well, tests at pH 6.8.

My chemistry degree was 25 years ago, and I no longer work in that field so I'm a bit rusty, but I look up the pKa of carbonate buffer, and find it is 6.35 & 10.33 with a useful buffering range of 6.0 - 8.0 and 9.5 - 11.0. For Borate, the pKa is 9.23 with a useful range of 8.5 - 10.2.

I assume the lower pKa for carbonate is the bicarbonate state, and the higher for the carbonate.

What I can't understand is how a borate addition would _decrease_ the number at which the buffer tends to hold the pH--since its active buffering range is higher than that of carbonate.

What am I missing?

As an aside, can anyone point to current, accurate resources for operating at higher pH levels? I have the info from the older Pool Solutions site, but wondered if there's anything more up to date.

Chuck