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Thread: loss of CYA

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    loss of CYA

    I maintain a pool in which the fill water is from a well which puts lots of metal in the pool. So much metal that the pool turns green whenever a few inches of water is added, and then clears up after a few hours. When i started servicing the pool the cya was up around 80, a few months later i tested and it was around 40. I didn't think much of it at the time because nothing was wrong with the pool, so i figured it was a bad test. About a month ago there was some algae in the pool and i test the cya and there is zero. I brought this up to the homeowner and she said oh yah this is normal, my old pool service would charge me yearly for more cya. This seems really strange. Is it possible that the metal is getting rid of the cya? There are no leaks in the pool. She has recently put a metal trap on her fill line, but it hasn't been long enough to notice whether or not this stops the loss of cya.

    Another pool, i did a stain removal and got the guy a vacuum, tested his water, the cya was over 100. I told him he needs to quit adding tablets and only add liquid. Anyway he calls a few months later says hes having problems and that the chlorine is only lasting a day, i go and test the water and theres no cya. The pool wasn't drained, and no leaks.

    Both of these maybe had a small amount of algae, but never a swamp, and it seems never long enough for algae to consume the cya. Any thoughts?

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    Mod Squad zea3's Avatar
    Join Date
    Jul 2009
    Houston, Texas

    Re: loss of CYA

    If they have sand filters that they backwash frequently, vacuum to waste often and they are not using chlorine that contains CYA then the levels of CYA will drop as the water is replaced. As far as I know the only other thing that will acount for CYA loss is bacteria that breaks down the CYA and leaves ammonia as one of the by products. Fertilizers in the pool may do this too. Ask about their vacuuming and backwashing habits, and get an ammonia test from a store that sells aquarium supplies.
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    Re: loss of CYA

    neither have backwash valves

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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: loss of CYA

    CYA is only removed from the pool through mechanical means....splashout, backwash, etc. It is not consumed by anything (there is an exception to that but it is not pertinent in your case).

    either through an autofill, splashout or some type of physical displacement, it is being lost. algae does not consume CYA
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: loss of CYA

    It's certainly possible that metals could catalyze the oxidation of CYA, but there's nothing explicitly documented about this that I could find. There is a slow oxidation of CYA by chlorine that is known, but whether metal ions catalyze this is not known. Certainly, letting the pool go to near-zero chlorine such that bacteria can grow can certainly degrade the CYA. Both of these processes are described technically in the thread Degradation of Cyanuric Acid (CYA).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Join Date
    May 2011
    Montgomery, TX

    Re: loss of CYA

    i had a similar loss of cya in my pool this year. i had been using my puck feeder and i checked the cya one day (around the end of june) and it was at 70. i thought that was borderline too high so i quit using the pucks and used 6% bleach only (and ma to control ph) for the next 2 months. about a week ago i rechecked cya and it was around 35. my pool is around 22,000 gallon gunite and i have a cartridge filter. i do not backwash. have not had much rain this year. my kids and labrador retreiver do use the pool almost every day. pool receives full sun almost all day.

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