PH plateau?

Normally my pool runs on the high-side with ph; typically 7.8-8. I do my acid thing on Weds and Sats usually needing about 20 oz to keep the pool at 7.5.

I've noticed lately, when I'm lazy and forget to check/adjust ph, it lowers on its own. What's up with this? This weekend, (after being lazy for 2 weeks), I checked my ph expecting it to be sky-high...it was perfect, 7.5.

I also noticed this in the middle of the summer. We were gone for 9 days. I was fully expecting to come back to really high ph readings--but it was perfect at 7.5...after 9 DAYS. I'm confused. Up to that trip, I was adding acid every 3rd day to keep ph in check.

What causes the ph to lower on it's own in a typically high ph pool?

Conditions:
Pool is uncovered...water temp is approx 52 degrees
I don't close the pool
I have lowered chlorine output on SWCG to about 3ppm for the winter

I can't explain what would lower the pH (and it really didn't sound like that was happening in your case anyway), but I can explain what would cause it to no longer rise as quickly or at all.

The rise in pH comes from the outgassing of carbon dioxide (pools are essentially over-carbonated -- that's mostly what TA is). The hydrogen gas bubbles produced in the SWG aerate the water and speed up this outgassing process. So lowering your SWG output slows down the rate of pH rise. Also, colder water temperatures outgas more slowly so that is also a factor.

Richard

Thanks Richard. It's almost like the more I leave it alone--the better it does!

Don't touch it ;)