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Thread: Black cobweb like dirt on bottom of salt water pool

  1. Back To Top    #1

    Join Date
    Jun 2014
    Franklin, Virginia

    Black cobweb like dirt on bottom of salt water pool

    Hello all,

    I have an in-ground salt water pool, 20x40 and I have to admit that due to school and working full time all summer I didn't have the time to tend to it daily like I should have. For the last part of the summer I've had to vaccum daily but about an hour after vacuuming the dirt like stuff would re-appear, so I'm really fed up right now. I want to close the pool for the winter but I need to make sure this is taken care of before I do it. First off, this guy that works for a pool company was unable to identify what it is. The thinks it's dirt. He claims it's not black algae but I don't think he knows what he is talking about. When I vacuum it, it disappears into fine mist. Is this black algae? Please help because i'm extremely frustrated! I've vacummed with both a pool blaster which is separate from the filter and I've also vacuumed through the filter/skimmer thru waste.

    32900 K Gal, IG, Vinyl, Hayward Aquarite Salt Gen, Sand, SWG, Manual vacuum cleaner

  2. Back To Top    #2
    Butterfly's Avatar
    Join Date
    May 2007
    South Carolina

    Re: Black cobweb like dirt on bottom of salt water pool

    Black algae is rare in vinyl pools. Also, you cannot vac it up! BA is bad and requires scrubbing just to knock off the head to allow chlorine inside to start the kill.

    I suggest you check your sand filter. You may need to do a deep cleaning, if you have not done one recently:

    You should also do an OCLT to help rule out/in organics as the problem:
    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.

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  3. Back To Top    #3

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Black cobweb like dirt on bottom of salt water pool

    Thorough advice always starts with a complete set of test results. Can you post those?

    Like Butterfly, I don't think it is black algae.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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