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Thread: Why is CYA increasing?

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    Join Date
    Jun 2014

    Why is CYA increasing?

    I just completed my first SLAM after 2 partial drains to reduce CYA. Got my cc down to .2, water is clear and passed the OCLT test. However, my CYA has increased the past few days after only using bleach for chlorine. I did have some old silk tabs in my feeder but the feeder was dialed to the 'off' position. Is it possible that caused my CYA to increase somehow? I cannot figure out what else would do it?

    Tues 6/23 CYA = 70
    Wed 6/24 CYA = 75
    Thurs 6/25 CYA = 75
    Fri 6/25 CYA = 80
    30,000 gallon, 20x40, IG, vinyl, sand filter

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    Mod Squad Texas Splash's Avatar
    Join Date
    Jun 2014
    South-Central Texas, Marion/San Antonio

    Re: Why is CYA increasing?

    I suspect that is possible any tabs left in your feeder could have continued to contribute to CYA. Even though they are dialed-down as low as they can go, water is still passing through that feeder, meaning anything inside is also dissolving. I would remove those tabs right away and stick only to chlorine as you have been doing. A CYA of 80 is high, but still manageable as long as you make sure your FC level stays at your target of 9. Never let it drop much lower than that (minimum is 6) because if you had to SLAM again (as you already know), it takes a lot of bleach at that CYA.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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  3. Back To Top    #3

    Re: Why is CYA increasing?

    Yes, even when set to zero (or "off"), the tablet feeders are designed to still allow a small amount of water to pass through, to prevent build-up of super-chlorinated water and chlorine gas.

    I don't recall where I learned that bit of trivia, but it is verified by my personal experience. And now yours as well.
    25000-gallon semi-public IG concrete/plaster pool, Triton II sand filter
    750-gallon semi-public IG concrete/plaster spa, cartridge filter
    Volunteer pool caretaker for my condominium complex

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    Mod Squad tim5055's Avatar
    Join Date
    May 2014
    Franklin, NC

    Re: Why is CYA increasing?

    While the feeder could be contributing, it could be that the CYA,is around 75. All the other numbers would be fairly close to the margin of error.

    Additionally, don't assign a true number to anything between marked readings. The scale on the tube is not linear, so half way between two numbers is not half the difference.
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  5. Back To Top    #5
    DaninFLA's Avatar
    Join Date
    Apr 2015
    Sarasota, FL

    Re: Why is CYA increasing?

    the CYA test is subjective and is also +/- 10 ppm minimum. so really your CYA is probably the same and the variation (well within the margin of error by the way) is just a result of difffernt lighting condition and/or how you read the dot being completely gone.
    9,000 gallon in-ground Saltwater pool, plaster, cartridge filer, 1.0 hp pump, Hayward T-15 SWCG, TF-100
    Pool School - Chlorine / CYA Chart; Pool School - Test Kits Compared;

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