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Thread: What causes PH to decrease?

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    flyboy320's Avatar
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    Jul 2009
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    Burlington, Ontario, Canada
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    What causes PH to decrease?

    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?
    10K gal IG, vinyl, 1 HP Jandy Stealth pump, Jandy CS cartridge filter, Delta UV system, Hasa Liquidator

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    frustratedpoolmom's Avatar
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    May 2007
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    SWSuburban Chicago, IL
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    Re: What causes PH to decrease?

    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
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    flyboy320's Avatar
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    Jul 2009
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    Burlington, Ontario, Canada
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    Re: What causes PH to decrease?

    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...

    Thanks....
    10K gal IG, vinyl, 1 HP Jandy Stealth pump, Jandy CS cartridge filter, Delta UV system, Hasa Liquidator

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    Join Date
    Mar 2007
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    San Rafael, CA USA
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    Re: What causes PH to decrease?

    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.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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