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Thread: CH levels, pitting and black spots

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    Join Date
    Jul 2011
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    New Orleans, LA
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    CH levels, pitting and black spots

    First let me start by saying that I inherited this pool and most, if not all of the pitting was there when I got it. But it could have gotten worse in the last couple years.

    I have some pitting and some etching going on and now they appear to have a black color to them. I assume this is residual algae but I'm not sure. (I had the current limiter recently quit on my SWG)


    What causes this pitting and can anything be done to repair it in the short run? (Absent a plaster job) I think my CH is fairly low, but was at a good level last year. I'm in search of the right thing to add, from the right place.

    Is the black stuff algae? And how can I get rid of it? I've tried scrubbing and pressurized water. It helps a little, but not much.

    FC 5
    CC 0.5
    PH 7.6
    TA 110
    CYA 40
    CH 170
    NaCl 3000

    I know my CYA is a little low and my TA is a little high, I'm working on getting those in check now. All advice is appreciated!
    25k gallon rectangular, Cartridge filtered
    New AquaRite T-15 cell and board
    IG Plaster, No idea of pump size/flow rate
    TF-100 kit with the K-1776 salt kit
    Polaris 280
    Still learning, but I've been to pool school!

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    JasonLion's Avatar
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    May 2007
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    Re: CH levels, pitting and black spots

    There are different kinds of pitting. The most common kind is from some combination of low PH, TA, and CH levels, where calcium is leached out of the surface and into the water. You can also get small pits from imperfections in the plaster.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3

    Join Date
    Jul 2011
    Location
    New Orleans, LA
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    Re: CH levels, pitting and black spots

    Is there anything I can do about it? What about the black spots? Here are some closer pictures

    Side wall


    Steps


    The majority of this occurs in the shallowest area of the pool and steps
    25k gallon rectangular, Cartridge filtered
    New AquaRite T-15 cell and board
    IG Plaster, No idea of pump size/flow rate
    TF-100 kit with the K-1776 salt kit
    Polaris 280
    Still learning, but I've been to pool school!

  4. Back To Top    #4

    Join Date
    Jul 2011
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    Arizona & California
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    771

    Re: CH levels, pitting and black spots

    If the black spots are black algae, try sprinkling some granular chlorine on the spots, either Cal hypo or Dichlor granular.

  5. Back To Top    #5
    Mod Squad jblizzle's Avatar
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    Re: CH levels, pitting and black spots

    Try scrapping some of the black off with a fingernail and smear it on a piece of paper. It would look green on the paper if it is algae.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Butterfly's Avatar
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    Re: CH levels, pitting and black spots

    You need to scrub the algae w/an algae brush. If it is black algae (looks like it to me) the algae brush is needed to knock off the heads of the algae so the chlorine can get inside for the kill. Scrub it before you add chlorine.

    Be sure to keep up with which chlorine you are using and how much of what (besides chlorine) you are adding to your pool. You can use the CalHypo until you get the CH in line, then switch to bleach/liquid chlorine. You can also spot- scrub smallish spots with a trichlor tab alternating with algae brush.

    You will need to follow the SLAM black algae process with elevated FC levels. See article in Pool School.

    Also, for regular brushing for you pool, I suggest a combo brush.
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