Water Temperature affect on pH level and danger


Platinum Supporter
LifeTime Supporter
Jun 28, 2011
Westford, MA
Hi all, just opened the pool this weekend in MetroWest Boston. Pool temperature was about 48, rising to mid-50s now. pH reading is well above 8.0. During the summer, I keep it in around 7.5 or so. I notice each year when I open the pool, pH is well above 8.0.

Two questions:
- what affect (if any) does water temperature have on measuring pH.

- while I know too high/low pH is bad for plaster, is this danger reduced because the water is so cold? If not, should I try to do something over the winter to limit the pH rise?

Thanks all

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
PH tends to rise in the cold water. The good thing is that cold water itself tends to help counter the effects of that pH rise in the overall balance of the water. What you asking is a need to understand how your pH, water temp, TA, and CH are working together throughout the year (hot versus cold). When you enter all those numbers into PoolMath, you'll see a "CSI" reading that helps to show you how well all those TFP parametes are working together. Notice how the pH and water temp have the most immediate impact on that "CSI" level and a pool water's potential to promote scale or become aggresive to the plaster. By understanding that relationship, you can see how important it is to control pH rise in the hotter months to prevent scale, and how in really cold water, an elevated pH isn't the worst thing.