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Thread: Accuracy of ph tests?

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    Accuracy of ph tests?

    So I tested my water at a pool store a few weeks ago. (said ph was 7.4)

    Then I had been using those 10$ 4 way HTH test strips they sell at my local Walmart. ph seemed to be 7.2 but I was worried the strips weren't accurate. So I bought a drop based ph and chlorine test.

    Are all phenol red ph tests kits made equally or are some better than others? As I am getting what seems to be an 8.2 and strips still look 7.4ish...

    Thanks!
    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: Accuracy of ph tests?

    Some of the phenol red PH tests are much more sensitive to the FC level than others. When FC is high (how high that is varies from brand to brand) the sample will turn a sort of purple color that is similar to the 8.2 color but is actually something else. The Taylor tests are fine up to an FC of 10, more or less right but read higher than actual up to almost 20, and that special purple color above that, but some of the cheaper tests can go to that special purple color with FC as low as 5.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Accuracy of ph tests?

    Eep!

    The strips read 3'ish (turns purple) but the drop based kit is yellow and looks darker than the 3 (max on the scale) so in the meantime I guess I could wait for the chlorine to test ~1-2 and retest ph? Until I get a better test kit that is....
    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
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Accuracy of ph tests?

    That sounds like a good plan.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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