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Thread: pH test changes after a few mins?

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    pH test changes after a few mins?

    Just curious what it means if I get a ph reading of 7.6 but after about 4-5 min in the tube its showing as 8.2?
    20,000L (5,200 gal) round AG pool, Hayward sand filter, 1.5hp pump, in the Laurentians, Quebec Canada
    Pool gets medium amount of sun, due to the house and surrounding trees.

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    JasonLion's Avatar
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    Re: pH test changes after a few mins?

    It means your PH is 7.6. The reading is correct for the first 30 seconds to a few minutes (the exact time varies) and after that it will often drift.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: pH test changes after a few mins?

    I have found that under conditions of FC greater than 10 ppm, and significant levels of CYA, the conversion of phenol red to chlorophenol red can happen, but at a delayed rate depending on the FC/CYA ratio. If the pH appears to go over 8.3 (purple), then this is the likely case.

    If the FC is greater than 10 ppm, and there is no CYA, then the conversion happens almost instantly.

    If the FC is below 10 ppm, then the sample pH can rise due to carbon dioxide offgassing.

    Therefore, as Jason noted, the reading needs to be taken immediately.

    What were the FC and CYA readings at the time?

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    Re: pH test changes after a few mins?

    CYA is 30 and FC 5
    20,000L (5,200 gal) round AG pool, Hayward sand filter, 1.5hp pump, in the Laurentians, Quebec Canada
    Pool gets medium amount of sun, due to the house and surrounding trees.

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