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Thread: Unexplained CYA drop ?

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    Join Date
    Mar 2014
    Location
    Hudson valley NY
    Posts
    20

    Unexplained CYA drop ?

    Hi,

    I had a long weekend away from home where my FC dropped to zero and the pool got cloudy. Prior to the algae cloudiness I had measured 35ppm CYA and was losing ~3ppm FC/per day (last season at 80CYA I was only losing 1ppm CYA/day). I had mostly returned the pool to clarity (pool was almost crystal last night, shocked +8ppm, and it was 4ppm in the morning so I guess I need to increase the frequency of my shocks so it's more like the SLAM process). But anyway, a few days ago during my shocking process I measured <20ppm CYA. I can't explain how the concentration dropped so much. Would a 3 or 4 day algae outbreak cause a CYA consumption like http://www.troublefreepool.com/threa...ric-Acid-(CYA) (this happened to me over the winter, but that was a winter's worth of green slime, not blue cloudy water). I had some heavy rains but based on some calculations only enough to drop the CYA a few ppm.

    My CYA reagant is about 1 year old, and I keep in a cool inside place, so I think that is ok. I suppose I could buy the standard for CYA, but avoiding money spent on my pool is always a plus

    Basically all I want to know is if you think I should be adding more CYA to the pool or not. I don't want to overdo it on CYA and then have to drain the pool.
    ~20k gal inground vinyl lined pool
    Hayward Perflex DE filter
    Aqua bot cleaner

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    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,085

    Re: Unexplained CYA drop ?

    read "The ABC's of Pool Water Chemistry" up in Pool School. Algae does not consume CYA....actually has no affect on it. Algae consumes chlorine but not CYA.

    I would not add any more CYA. I think your first, most economical step, might be to report a complete set of test results and see if we can help figure out what's gone awry.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  3. Back To Top    #3

    Join Date
    Mar 2014
    Location
    Hudson valley NY
    Posts
    20

    Re: Unexplained CYA drop ?

    ~18.3k gal currently
    Added 4500 mL 12.5 bleach 30-45min before test (~+8ppm)

    FC - 6.5ppm
    CC - 0.5-1ppm
    pH - 7.9 (probably high from bleach, reading 2 days ago 7.5)
    TA - 100-110ppm
    CH - 160
    CYA < 20 (35ppm 2.5 weeks ago)
    ~20k gal inground vinyl lined pool
    Hayward Perflex DE filter
    Aqua bot cleaner

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