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Thread: CYA went down over the winter?

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    CYA went down over the winter?

    Hi All,

    Last summer was my first summer at a new house that had a pool. The prior owner used chlorine pucks and the CYA was very high all summer, in the neighborhood of 95. Pool School says the typical way to reduce CYA is to drain and replace water. I got tired of that after replacing about 12 inches of water, so I just used lots of bleach as called for in the calculator and the pool was fine but the CYA stayed high all summer. So far no surprises. But this summer, I just opened the pool and it balanced very quickly and got very clean very fast, but my first test of CYA reads 35 or maybe 40. Is there an explanation for how the CYA went down over the winter? If relevant, I live in central Virginia.



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    Mod Squad JohnT's Avatar
    Join Date
    Apr 2007
    SW Indiana

    Re: CYA went down over the winter?

    It's pretty normal to lose quite a bit over the winter. I lose all of mine every year.
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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: CYA went down over the winter?

    Seems to sometimes happen over winter. One theory is a bacteria breaking it down into ammonia. But does not sound like you saw a lot a CC as is typical of ammonia.

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    Jason, TFP Moderator
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    In the Industry

    Join Date
    Feb 2012
    Phoenix, AZ

    Re: CYA went down over the winter?

    I am not sure of the chemistry behind it, but this is not uncommon. Enjoy this pool season with much less chlorine use!

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    Butterfly's Avatar
    Join Date
    May 2007
    South Carolina

    Re: CYA went down over the winter?

    Hi Gene and welome to the forum

    Use the google search (bottom left on page) for disappearing cya. Lotsa threads around if you'd like to do more reading.
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  6. Back To Top    #6

    Re: CYA went down over the winter?

    Thanks everybody. It is good to see that this happens to others. I will do the Google search and read up about it, but in the meantime, I'm glad to hear that it is at least possible that my testing was accurate last year and this year. Plus I can take the station wagon instead of the pickup to buy bleach, right?

    Happy swimming!


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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: CYA went down over the winter?

    Depending on the bacteria, the CYA can get broken down to ammonia or it can get broken down to nitrogen gas (see Degradation of Cyanuric Acid (CYA) for technical details). So upon spring opening you may a huge chlorine demand where adding chlorine produces a lot of CC from ammonia, or you may have no chlorine demand and a nice pool with lower or zero CYA in it. If we could only figure out a way to bottle the proper bacteria and have them do what we want when we want... Actually, it turns out that some waste water treatment of sludge does involve intentional dosing with bacteria and varying oxygen levels to break down organics similar to CYA all the way to nitrogen gas, so it's not that far-fetched.
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