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Thread: Help with rust looking stains

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    Help with rust looking stains

    Tried a quick search but this topic is so varied. I have rust looking stains appearing at the bottom of my plastered pool. Not on the walls, just the bottom in random places. I put some vitamin C tablets on one of the stains and it actually turned darker! I jumped in my cold pool and attempted to wire brush it to no avail. I tried pouring bleach on a rag and holding it on the stain. Nothing.

    I should add that I had something similar happen to me last year around this time. I didn't do anything and they ended up disappearing. But this year, there are many more stains.

    What now? These are really ugly.

    My FC is 6 ppm, pH was at 8, I've added some acid to bring back down and haven't retested. Alkalinity is 70 ppm.
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    IG 14,000 gallon, plaster, SWG Pentair IC40, cartridge filter, S/U April 2012

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    JasonLion's Avatar
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    Re: Help with rust looking stains

    Stains that turn darker when you try vitamin C are often copper. Have you used any products containing copper (a few algaecides, ionizers, mineral cartridges, etc)?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Help with rust looking stains

    No sir. I've been a BBB guy since we got the pool (only 2 years old). I did take a sample of water to Leslie's to test for metals and they didn't find any for what that's worth. Is there something I can do to test if the stain is copper? I'm not sure where the copper would have come from.

    Also - I did introduce borates last season using the 20 Mule Borax addition. Don't think that's related but its part of my pool chemistry.
    IG 14,000 gallon, plaster, SWG Pentair IC40, cartridge filter, S/U April 2012

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    Re: Help with rust looking stains

    I did some additional research on the site. I'm going to pick up some dry acid and try putting it on the stain. I understand that is the method for Cu testing. If that doesn't work, I'll pick up a Jack's Magic test kit and go thru it for identifying what the stain is.

    If I'm on the wrong path, please let me know.
    IG 14,000 gallon, plaster, SWG Pentair IC40, cartridge filter, S/U April 2012

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    Mod Squad JVTrain's Avatar
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    Re: Help with rust looking stains

    Is there a chance that the rebar in the concrete behind the plaster is not embedded deep enough and it is being wetted by pool water through the surface and rusting the rebar?

    I don't have any knowledge of the pool build or much knowledge on how pools are built or otherwise but if it's just on the bottom, perhaps when the pool was built, the rebar/steel framework was not deep enough in the concrete or rose prior to fully curing?
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
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    Re: Help with rust looking stains

    I'm sure I'm just projecting my problems, but that spot looks like the stains I sometimes get from oak pollen. Or something related to those oak flowers falling in the pool. I'm never exactly sure why sometimes they stain and sometimes they don't. They form very fast and take a week to fade away. I have a bunch right now as our trees are at maximum flower dumping. I haven't tried putting trichlor on them, because I already know they're organic.
    20,000 gal in-ground plaster pool with sand filter. Replastered recently. Mostly adding bleach and acid. CYA was high when I took over.

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    Re: Help with rust looking stains

    I dunno. I had this issue last year and the stains went away on their own. I would not believe its rebar but never know......

    As far as trees, I have the pool surrounded by Queen Palms and Birds of Paradise. Don't think anything is from that. But again nothing for sure.

    I did the dry acid trick. It is picking up the stain. Makes me wonder if I let the pH drift too high and that precipitates these stains.
    IG 14,000 gallon, plaster, SWG Pentair IC40, cartridge filter, S/U April 2012

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    Smykowski's Avatar
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    Re: Help with rust looking stains

    That might be it. You could try running your pH at 7.2-7.4 for a bit to see if that helps. Can you post a full set of test results so we can see where you're at now?
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
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    Re: Help with rust looking stains

    Per request - some readings. I did lower the pH a bit intentionally. But no worries with a SWG, it will drift back into range soon.

    pH = 7.2
    Alk = 50 ppm
    FC = 9 ppm
    CC = 0.5 ppm
    CYA = 40 ppm
    Borates = 50 ppm
    IG 14,000 gallon, plaster, SWG Pentair IC40, cartridge filter, S/U April 2012

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