Just to add to what Watermom said, if you had a really heavy rain, that could have aerated the water enough to bring the pH up a little bit. The TA in my pool is 110, and my pH rarely moves from 7.8, unless I do something (like add acid) to move it. In most cases, though, it's right back to 7.8 within a day or two, because that's the pH of my fill water. I tried to fight it for the first couple of years, but then I realized I was just wasting time and acid!

Janet