What causes PH to decrease?

[flyboy320]

I've got a fairly new IG pool, (open about a month), and have noticed the PH slowly decreases. It started at about 7.5, and over the last few weeks has drifted down to 7.2. Thanks to this web site, I'm not worried about it and have been using BBB with great success since it was built, but I'm just wondering what can causes this?

 

[frustratedpoolmom]

What is your TA?

If you keep the pool covered when it's not in use, that prevents it from outgassing and the PH will decrease.

Or something like that....LOL

 

[flyboy320]

TA is 90.

I have had the cover on quite a bit the last two weeks or so to help keep the pool warm overnight, so that may be the cause... :lol:

Thanks....

 

[chem geek]

Are you using any Trichlor or Dichlor for chlorine or are you using any non-chlorine shock? All of these are net acidic. If you are only using a hypochlorite source of chlorine (chlorinating liquid, bleach, Cal-Hypo, lithium hypochorite), then the pH is normally stable or rising. A falling pH is usually associated with some type of acid getting added to the pool. The pH will also fall somewhat after a shock as the Free Chlorine (FC) level drops.