High pH

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Bill C

High pH

Postby Bill C » Mon 11 May, 2009 22:13

I have an outdoor pool with a pebble-tech finish. I installed a salt-water chlorine generator about 6 months ago and have been having problems keeping the pH within limits. Though the water used to top-off the pool (for evaporation) has a pH of 7.5, the pool pH keeps rising quickly despite the use of muriatic acid to bring it back down. Within a few days of adding acid, the pH rises from 7.4-7.5 to around 8.0.

Does anyone have any suggestions?


chem geek
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High pH

Postby chem geek » Tue 12 May, 2009 03:12

Read Water Balance for SWGs . You need to keep your Total Alkalinity (TA) lower, probably around 70 ppm, and you should have your Cyanuric Acid (CYA) fairly high at 70-80 ppm and your target Free Chlorine (FC) at 4 ppm. You can also use 50 ppm Borates.
Me...
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High pH

Postby Me... » Tue 12 May, 2009 08:58

I am thinking a bit different on this one. While I agree on keeping the TA down a bit lower than normal I would still only keep the CYA at about 30-40. Having a higher CYA ties up the chlorine forcing your cells to produce more chlorine in order to compensate and do the the job as say 2ppm. The more your cells are on producing chlorine the more they are driving up the pH. Adding acid to keep the pH down will also start depressing the alkalinity. What is the Alkalinity of your fill water by the way?

I am sure Chem geek has the science and math at his fingertips and I am also sure he is now going to post it for us :D
chem geek
Pool Industry Leader
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Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

High pH

Postby chem geek » Tue 12 May, 2009 09:44

For an outdoor pool, we found that the higher CYA protects the chlorine from sunlight in a non-linear way so that even with a higher FC level for the higher CYA level the net chlorine usage is lower so the SWG ontime can be set lower and that results in less bubbles from the SWG and less chlorine outgassing, all resulting in a slower pH rise.

For a pool not exposed to the sun, then I would agree with you that a low CYA is fine.

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