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Thread: Fighting stains that turn black after adding shock.

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    Join Date
    May 2016
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    Hammond, LA
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    Angry Fighting stains that turn black after adding shock.

    This is my first post with this group. I had stains appear during the winter. Pool center said high in minerals. As a result of several conversations, we disconnected the ozone system and Nature2 system. Changed the sand. Water is clear but stains won't leave. When I add shock the stains go to a darker gray or black. Won't stub off. Over 24 hours, darkness fades, but stains are still there. I am truly stumped. Am I fighting algae or metals or both? Getting different recommendations from pool centers. We have a leaf problem in the winter, which we skim up. Pool runs all year long. This is the first time we have had this problem in 5 years. Even the return gets have turned a dingy yellowish brown. I hope someone can help me. Thanks
    ​Dr. G. 17k Ig, plaster, 5 years, sand filter, 1/2 hp whisper pump, Polaris 250 cleaner. LaMotte 2056 tester kit

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    AimeeH's Avatar
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    Re: Fighting stains that turn black after adding shock.

    Welcome to TFP.

    A couple of things to try:

    Rub a vitamin C tablet on the stain. If that shows improvement you probably have a metal issue

    Rub a chlorine puck on the stain. If that shows improvement you are likely dealing with algae.

    How are you chlorinating your water? And posting a full set of test results will help us help you.
    18*36*23 true "L" vinyl IG 29,000 gallons. SWG. TF-100 test kit.
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    Re: Fighting stains that turn black after adding shock.

    Tried the test you recommended. It seems that this is algae after all. Tested the water: total alk:101.00ppm; pH: 7.30; temp: 89.1; Cal H: 203.00 ppm; FC 2.53 ppm; Stab: 75.00 ppm. What are your suggestions?
    ​Dr. G. 17k Ig, plaster, 5 years, sand filter, 1/2 hp whisper pump, Polaris 250 cleaner. LaMotte 2056 tester kit

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    Richard320's Avatar
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    Re: Fighting stains that turn black after adding shock.

    Quote Originally Posted by drgarymartinez View Post
    Tried the test you recommended. It seems that this is algae after all. Tested the water: total alk:101.00ppm; pH: 7.30; temp: 89.1; Cal H: 203.00 ppm; FC 2.53 ppm; Stab: 75.00 ppm. What are your suggestions?
    Hopefully you tried the Vitamin C first. It lifts metals but not organics. A Trichlor puck will lift either. So you might have just given yourself a false positive for organics when it's metals. Vitamin C will work fast -- check out the picture here: Yellow Stains

    If it is organic, then time and chlorine will lift it. You just have to maintain the FC/CYA ratio and be patient. I suspect it's metals because it darkens with chlorine.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
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