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Thread: Huge Black stain in deep end bowl

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    Huge Black stain in deep end bowl

    Got a pool that sat for well over a year with nothing but disgusting water in it. Eventually most of the water evaporated and left a huge black stain in the deep end of the pool, as well as dark yellow stains all through the rest of the surface about halfway up the walls. Muriatic acid lightens the yellow stuff, but it is not touching the black stuff. Is there anything that can be done to get rid of the stain?

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    Re: Huge Black stain in deep end bowl

    Gunite or vinyl?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    JasonLion's Avatar
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    Re: Huge Black stain in deep end bowl

    That sounds like heavy organic staining. I would try resting a trichlor tablet on a stained area for half an hour and see what effect that has. If trichlor helps, you can keep the pool at shock level for a few days, or at worst weeks, to clean up the stain. If the trichlor does nothing, we will have to try some other approach.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Huge Black stain in deep end bowl

    it is gunite. The pool is empty right now. Would putting the tablet on the stain be more effective than pouring liquid on it and letting that sit? the only reason i ask is because i have already tried letting liquid chlorine sit on it

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    Re: Huge Black stain in deep end bowl

    So I assume you are saying the chlorine had no affect.

    There are two types or stains....organic and inorganic.

    Those stains respond to either muriatic acid (inorganic) or chlorine (organic)

    Your stain WILL respond to one of those two chemicals. Perhaps you are not concentrating it enough?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Huge Black stain in deep end bowl

    I have tried undiluted acid as well as undiluted liquid cl

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    Re: Huge Black stain in deep end bowl

    Well, there really is no third type of stain so if your stain is unresponsive to both muriatic and chlorine, I am at a complete loss
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Richard320's Avatar
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    Re: Huge Black stain in deep end bowl

    I wonder if it isn't a deeply embedded iron stain? Red rust can be turned into black iron oxide - like the finish on chisels and drill bits - with certain acids. That's what Naval Jelly does. The yellow stains might have been rust, and some genius might have tried pouring some rust remover into the pool.

    I have no solution to offer, unfortunately.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Re: Huge Black stain in deep end bowl

    I probably ought to clarify. The Acid lightened the staining of the yellow areas, not very good but it definitely lightened it. The black staining in the very bottom though was not fazed by anything.

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