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Thread: Black "oil looking" stains

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    tgenre's Avatar
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    Black "oil looking" stains

    HELP! I have a few black spots on my plaster that look like drops of black oil. I'm 99.9% sure I had nothing drip into my pool. I've had a couple of these for months that I ignored but now I have several that I think developed over the weekend. Is this common? Do you have any idea what it is? I've had the stains that come up with Vitamin C, but this is not that.

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    18k Gallon gunite with Diamond Brite Bahama Breeze, Intellichlor IC20 SWG, Intelliflo Variable Speed Pump, Pentair Clean and Clear

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    Richard320's Avatar
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    Re: Black "oil looking" stains

    Can you scrape it off with a fingernail? If so, do that and rub it on a piece of white paper. If it's actually dark green, it's black algae.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    tgenre's Avatar
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    Re: Black "oil looking" stains

    Will not scrape. And thanks for responding so quickly.
    18k Gallon gunite with Diamond Brite Bahama Breeze, Intellichlor IC20 SWG, Intelliflo Variable Speed Pump, Pentair Clean and Clear

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    tgenre's Avatar
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    Re: Black "oil looking" stains

    Any other suggestions?
    18k Gallon gunite with Diamond Brite Bahama Breeze, Intellichlor IC20 SWG, Intelliflo Variable Speed Pump, Pentair Clean and Clear

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    Re: Black "oil looking" stains

    Can you post pictures?

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    tgenre's Avatar
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    Re: Black "oil looking" stains

    At work now...will take pics tomorrow and post
    18k Gallon gunite with Diamond Brite Bahama Breeze, Intellichlor IC20 SWG, Intelliflo Variable Speed Pump, Pentair Clean and Clear

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    Butterfly's Avatar
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    Re: Black "oil looking" stains

    What type brush do you use and how often do you brush the pool? Does brushing lessen/lighten/make any difference with the spots?
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  8. Back To Top    #8
    tgenre's Avatar
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    Re: Black "oil looking" stains

    I do not brush often enough. I've never had anyone tell me how often I should brush (other than the initial twice daily brushing with fresh plaster). It is a Nylon (I think) brush. I probably brush the pool a few times a month, to be honest. The spots have actually lightened (although they wouldn't scrape with a fingernail or respond to vitamin C). They are still visible, and I have some that have been there for a while in the deeper end - those are still dark. I'm not sure about the metal content in my water, as I've not had a pool store test my water since being a TFP member!
    18k Gallon gunite with Diamond Brite Bahama Breeze, Intellichlor IC20 SWG, Intelliflo Variable Speed Pump, Pentair Clean and Clear

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    Butterfly's Avatar
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    Re: Black "oil looking" stains

    Brush recommendations:

    Nylon is for vinyl, fiberglass, tile, and plaster that is less than one year. (Plaster includes any exposed aggregate and marcite finish, btw!) Combo brushes are for older plaster. All stainless are for algae (very stubborn green algae and also the ONLY brush for black algae.)

    You CAN unscrew the Wall Whale from the nylon brush it comes with and screw it on a combo brush if your plaster is over a year old. Newer plaster is really too soft for anyting other than a nylon brush.
    Try rubbing a trichlor puck on the stain, or let it sit on the stain for a minute or two and see if it lightens.

    It would be good to brush the pool once a week. Most of us probably do not brush often enough.
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  10. Back To Top    #10
    tgenre's Avatar
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    Re: Black "oil looking" stains

    Thanks for the education. My plaster is 6-7 mo old, so I'm good with Nylon brush only at this time (I just need to use it . I'll try to get some trichlor tabs and see what happens.
    18k Gallon gunite with Diamond Brite Bahama Breeze, Intellichlor IC20 SWG, Intelliflo Variable Speed Pump, Pentair Clean and Clear

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