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Thread: **** black spots, be gone!

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    Join Date
    Mar 2013
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    Seattle, WA
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    **** black spots, be gone!

    Hi all, bought a foreclosed house a couple months ago, pool was pretty nasty, so it took quite a bit to get it usable. The service I worked with had me add 25lbs of baking soda, lots of chlorine, new filters, and 2 weeks of constant filtering. Wish I had the original tests but I've lost them (arg).

    Water looks great now and we've used it quite a bit, but for the life of me, I can't get these black spots out of the plaster and more seem to appear each week. The pool and spa also have splotches which I assume is plaster wear?? For the black spots, I've been mainly scrubbing (hard as ****) with a wire pool brush. I tried a crappy pool stone, but that did nothing but disappear in 30 sec.

    Recent test results (from pool service, using manual test with taylor kit):
    • TDS: 410
      CYA: 50
      Tot Chlorine: 8
      Free Chlorine: 8
      PH: 7.6
      TA: 140
      Total Hardness (?): 150


    This is my first pool so everything is new to me. Appreciate any tips you can spare, thanks!

    [attachment=1:yi6qec1j]pool.JPG[/attachment:yi6qec1j]
    [attachment=2:yi6qec1j]dirt1.JPG[/attachment:yi6qec1j]
    [attachment=0:yi6qec1j]bottom.JPG[/attachment:yi6qec1j]
    Attached Images Attached Images
    21K Gallon In Ground Pool with connected 500G spa, both plaster, built in 2001
    333K BTU Sta-Rite Max-E Therm Heater
    Pentair System 3 Cartridge Filter (300 sqft)
    Pentair WisperFlo 2HP pump
    Polaris Caretaker in-floor cleaning system
    pic: http://sdrv.ms/13Tqt2J

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    BoDarville's Avatar
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    Jun 2012
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    Re: **** black spots, be gone!

    Welcome to TFP

    Before you try too hard to remove those black spots, it's possible that they may have been added to the plaster intentionally as a non-slip surface to allow your feet a better grip, especially when entering or exiting the pool/spa. We have that in our current spa and when we first moved in (as a first-time pool owner) I thought it might be black algae. Pool service save me from myself at that time.

    BTW, your numbers look fine. You can ignore TDS - completely irrelevant to managing a pool.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
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    duraleigh's Avatar
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    Re: **** black spots, be gone!

    Black algae will scrape off (partially) with your fingernail and then, if you smear it on a white piece of paper, will appear as a dark, blackish green streak
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  4. Back To Top    #4

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    Mar 2013
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    Seattle, WA
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    Re: **** black spots, be gone!

    The spots are random throughout the pool, just more heavy near the step so I'm pretty sure it's not part of the design, but appreciate that warning.

    It's not coming off with heavy brushing, I also tried just smearing some paper towel on it, but nothing transferring to it so I don't think it's black algae either.

    I'm going try dropping some granular chlorine on it to see if that does anything. It's white plaster so I figure bleaching it can't hurt ; )
    21K Gallon In Ground Pool with connected 500G spa, both plaster, built in 2001
    333K BTU Sta-Rite Max-E Therm Heater
    Pentair System 3 Cartridge Filter (300 sqft)
    Pentair WisperFlo 2HP pump
    Polaris Caretaker in-floor cleaning system
    pic: http://sdrv.ms/13Tqt2J

  5. Back To Top    #5
    Butterfly's Avatar
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    May 2007
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    South Carolina
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    Re: **** black spots, be gone!

    Quote Originally Posted by duraleigh
    Black algae will scrape off (partially) with your fingernail and then, if you smear it on a white piece of paper, will appear as a dark, blackish green streak
    Quote Originally Posted by jamescl
    It's not coming off with heavy brushing, I also tried just smearing some paper towel on it, but nothing transferring to it so I don't think it's black algae either.
    We usually recommend paper like a business card stock. Not paper towel.

    Black algae does not 'come off' with heavy brushing. Black algae is a hard algae, hard as in must-knock-off-tops-w/stainless-steel-algae-brush hard, and then treat aggressively w/chlorine. There is more to learn about how to treat BA. You can use google, bottom left of each page.
    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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