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Thread: Black stain

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    Join Date
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    Black stain

    Hi everyone,

    I just pulled the cover off this morning and found a huge black stain in the deep end. The pool is a 20' x 40' gunite with about 36,000 gallons. The black stain is about 6' in diameter in the deep end of the pool. I tried brushing it with a small metal bristle brush and it came up slightly, but not significantly. The water is clear and there's a few misc leaves and such which made their way under the cover, but there's not a ton of debris in there.

    I'm thinking maybe a copper stain from the winterizer - I used two Winter Pills (Amazon.com : AquaPill - WinterPill 4 Garden) same as prior years - but have never seen this issue before.

    Any ideas what it might be?

    Dan
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    Re: Black stain

    Were leaves allowed to accumulate in the deep end? It could be tannic acid from the leaves if that is so.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Black stain

    I don't think so. I took the picture literally right after the cover was peeled back. I thought it was leaves at first too, but there's nothing in there.

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    Re: Black stain

    That's puzzling. So let's see if we can identify the stain. Get a puck (tri-chlor) used for chlorinating the pool. Tie it on a string and lower it until it touches directly onto the stain. Let it set for a couple of minutes, and then lift it up and out. I am hoping you will notice a circle (lighter) where the puck was. Tell me what you find.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Black stain

    Quote Originally Posted by duraleigh View Post
    That's puzzling. So let's see if we can identify the stain. Get a puck (tri-chlor) used for chlorinating the pool. Tie it on a string and lower it until it touches directly onto the stain. Let it set for a couple of minutes, and then lift it up and out. I am hoping you will notice a circle (lighter) where the puck was. Tell me what you find.
    I dropped a puck on there last night for about 5 minutes and it did lighten up significantly. When I pulled it up the lightened circle was clearly visible. What's the prognosis?

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    Mod Squad pooldv's Avatar
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    Re: Black stain

    That means it is an organic stain, which is good. Raise your FC up to close to shock level for your CYA, Chlorine CYA Chart, and brush as often as you can stand to.
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    2012 build and pics, 20k gal gunite, black onyx pebblesheen, OK flagstone, IntellifoVS, cart filter w/Pleatco, IC40 SWG, Solartouch, 5 12'x4' solar panels, HP50HA heat pump, 8mil solar cover, borates, TF-100 test kit, SONOS, Doheny's Discovery Robot, hot tub on bleach

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    Re: Black stain

    Quote Originally Posted by pooldv View Post
    That means it is an organic stain, which is good. Raise your FC up to close to shock level for your CYA, Chlorine CYA Chart, and brush as often as you can stand to.
    Awesome - thanks guys!

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    Re: Black stain

    That happens when organics accumulate in the deepest part. Quite often it's decomposed worms and some sort of bacteria. Shock and brushing should get it.

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