PH Question

[chem geek]

There is a technical discussion at this thread in the China Shop that explores why pH rises and what can be done about it. It's a long thread, but the bottom line is that the pH normally rises due to the outgassing of carbon dioxide. Pools are intentionally over-carbonated (like a tasty beverage!) as part of the pH buffering system from carbonates. When carbon dioxide outgasses (i.e. leaves the pool water and goes into the air) it raises the pH of the pool water.

This outgassing process is accelerated by aeration of the water, by lower pH, and by higher TA. This table gives a rough idea of relative rates, but aeration isn't part of the table so the actual rate of pH rise will be depend on the aeration. An SWG actually aerates the pool as the hydrogen gas bubbles that are produced are a form of aeration and pull out the carbon dioxide faster so typically SWG pools have more of a problem of rising pH than non-SWG pools.

The two easiest ways to reduce the problem of rising pH, other than reducing the sources of aeration, are to lower the TA using Ben's Lowering Your Alkalinity procedure and using 50 ppm Borates (from Borax) if you have an SWG since that lets you lower SWG output since the Borates are an algaecide so do some of the work that chlorine would normally do. You can also not try and fight the rise as much and keep your pool at a somewhat higher pH.

Richard

[cnk]

So how much Borax would I need to add for a 12,500 gallon pool? Do I need to bring the PH down before or after adding the Borax? I tested my tap water & it has a PH of 7.2 so it's not naturally high.

[waterbear]

So how much Borax would I need to add for a 12,500 gallon pool? Do I need to bring the PH down before or after adding the Borax? I tested my tap water & it has a PH of 7.2 so it's not naturally high.

3 3/4 lbs of borax and 1 at of muriatic acid per 1000 gallons will raise the borate level to 50 ppm and bring the pH back to normal range (actually it's 3 lbs 11 oz of borax and 3 cups and 6 oz of acid if you want to be more exact but that is a lot harder to measure!).
Since a normal box of borax has 76 oz in it you would need 9.5 boxes and 3 gal of acid to bring your pool to about 50 ppm borates amd bring the pH back in line.
Add about 3boxes and a gallon of acid, brush the pool to mix and dissolve them, add another three and another gallon of acid and brush, then add the rest and brush.
The borates will not go away unless you drain the pool so you really don't hve to do this. I added borates to my pool last july and the levels are still fine. You want 30 -50 ppm borates. I use the AquaChek borate test strips that I buy online. LaMotte and Proteam also make borate test strips.
For more info check out these two threads:
http://www.poolforum.com/pf2/showthread.php?t=4712
http://www.poolforum.com/pf2/showthread.php?t=5419

BTW, I have not needed to add ANY acid to my pool for the past 3 months! pH has held steady at 7.6, TA at 80 (pool is NOT closed, I live in Fl).

Edit: Also,I have ordered the Aquacheck strips from here
http://www.diywatertesting.com/
Cheapest price I could find, free shipping, and I got my oder in 3 days!

[cnk]

Thanks! This will be very helpful.