I am using a cover over the pool. Leaves do get on the cover. The cover however is a few years old and I suspect rainwater migrate some from the cover to the pool and vice versa. So I guess this is a possibility. And yes rainfall has been more than normal this year, but this was a problem last year as well. I have not checked the pH of our rain but will do that next time it rains. I will also check the pH of the water that is on top of my cover.

One other question. Since this is an A/G pool I do not worry about alkalinity. I used to think that alkalinity stabilized my pH but through testing I concluded it does not...at least for vinyl liner pools. See this string of posts - http://www.poolforum.com/pf2/showthread.php?t=7870. My question is, would increasing the alkalinity at the time I close the pool help keep pH from dropping or should I just keep a closer eye on pH and adjust ever month or so?

Thanks again for the help.

Jim