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Thread: CYA Testing in the morning vs. afternoon

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    CYA Testing in the morning vs. afternoon

    Is there an optimum time of day to test CYA levels? If I test mid-morning, back to the sun, I get a higher CYA reading than when I test the same way in the afternoon.
    Indiana, 20k gallons, in-ground, vinyl, 1.0hp whisperflow pump, sand filter

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    benavidescj's Avatar
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    Re: CYA Testing in the morning vs. afternoon

    What are the two readings?
    Carlos
    Pool: 28,000 gallons IG; IC 40 SWG; Pentair 120 gpm cartridge filter; Marble finish; Pentair Wisperflow 1.5 hp; Polaris 360
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    Re: CYA Testing in the morning vs. afternoon

    Mid morning was about 55-60

    Afternoon was about 65 to 70
    Indiana, 20k gallons, in-ground, vinyl, 1.0hp whisperflow pump, sand filter

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    Re: CYA Testing in the morning vs. afternoon

    Maybe user error? Try testing indoors (like a basement) using only artificial light that way it should take out any sun factor.
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    Re: CYA Testing in the morning vs. afternoon

    I always test mine in the afternoon on a sunny day. I will sit in a shady spot to take my reading. Because of these types of variances and the subjective nature of the test, testing the same way each time works out best.

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    Re: CYA Testing in the morning vs. afternoon

    Since the margin of error on the CYA test is plus or minus 10ppm, those test results are essentially the same. Call it 60ppm and you're good to go.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: CYA Testing in the morning vs. afternoon

    Apparently, the intensity of ambient light has the potential to skew the test. (See the quote below)
    Quote Originally Posted by JasonLion
    With significant amounts of practice, and proper outdoor lighting, most people can get repeatable results that give the same answer +-5. But the test it's self isn't really that precise. The CYA test is about +-15 when you are doing it correctly. Novices often stop early, when the black dot is kind of mostly obscured, which can give results that are 20 or 30 ppm higher than what they would get if they were doing it correctly. Reading the test indoors seems to result in numbers that are 10 or 20 ppm higher than otherwise.
    But for me, I believe I get the best results from reading the test indoors, in front of a west facing full length window, in the afternoon. This way I get the benefit of strong indirect light, but I avoid the glare that I get when I try to read the test outdoors.
    20K gal IG plaster pool, Manually chlorinated with 6% bleach, 1.5 HP Sta-Rite Dura-Glas II pump, Pentair FNS Plus 48 DE filter, Polaris 280

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