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Thread: Mysterious stains in deep end of pool?

  1. Back To Top    #1

    Join Date
    Jul 2009
    Charlotte NC

    Mysterious stains in deep end of pool?

    I was playing a fetch game with my kids yesterday with swim goggles and when I went to the bottom in
    the deep end I noticed several tiny ( BB-size) blackish spots which did not come off when rubbed. In fact
    some of them appeared to be eating away at my liner as they felt indented. I managed to pick up a BB size
    blackish ball and bring it to the surface. It was very hard. My concern is my liner. Has anybody ever heard or
    seen anything like this? I have not added any type of solid chemical for weeks ( salt being the last,but I always
    predissolve) and as far as I know the kids havent put anything in. I do have alot of trees around but cant
    imagine anything that could stain let alone eat away at vinyl. Thanks
    16x34 kidney shape 19,000 gal vinyl IG
    Pentair IC-20 SWG
    Pentair sand filter
    Pentair 1HP pump

  2. Back To Top    #2

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Mysterious stains in deep end of pool?

    See if it dissolves in a mild acid solution. If it does, and especially if it fizzes when acid is added to it, then it is probably calcium carbonate. Usually that's more gray than black, however, but it could have picked up dirt or something else in the water to become darker. Check your saturation index to see if it's high using The Pool Calculator.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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