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Thread: I have dark stains on the surface of my gunite pool

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    I have dark stains on the surface of my gunite pool

    I have dark stains on the surface of my gunite pool. The water temp here is about 55F which is not ideal for testing for stains, but I am in a hurry so I went ahead and used Jack's Magic Stain Identification Kit. Results were a little inconsistent (the water temp should be above 65 F for accurate results). In one area, the 'green stuff' worked but not in another area I tried. It is for copper and scale stains. Little bubbles formed as it was working which the person at Jack's Magic help line said indicate Calcium stains. He also said that given the low water temp and inconsistent results, he would not recommend using the 'green stuff' stain remover at this water temp as he could not guarantee satisfactory results. I am in a hurry and don't want to wait for the water to warm up. He said another possible treatment is to lower the pH (really low) and brush the pool walls daily. (He recommended adding 12.5 gallons of muriatic acid - in a 25,000 gallon pool) He said that this method could take a week and that twice daily testing for CH would have to been done to ensure that the plaster on the pool walls was not dissolving. He said a spike in CH would indicate a problem, the pool would then have to be 1/2 drained and refilled.
    He said another alternative would be to drain and acid wash the pool.
    I need to try to take care of the stains in the next couple days.
    Any other suggestions? What is the best way to get rid of stains due to calcium deposits?. Last spring after being away, my TA was sky high and I assume this is what caused the Calcium to precipitate out of solution and stain the walls. Does the ascorbic acid treatment work for calcium?
    If I lower the pH and brush, will that help? If so, how low should I go?

    Thanks!
    25,000 gallons
    gunite pool well over 10 years old?
    FAC 0 (deliberatley low to meet stain test kit parameters)
    TAC 0
    CH 275
    TA 60
    pH 7.2
    Temp 55 F
    location TX

  2. Back To Top    #2

    Re: dark stains on surface of gunite pool due to calcium dep

    Sorry I forgot above to add that the cya is around 15 - 20

    I have dark stains on the surface of my gunite pool. The water temp here is about 55F which is not ideal for testing for stains, but I am in a hurry so I went ahead and used Jack's Magic Stain Identification Kit. Results were a little inconsistent (the water temp should be above 65 F for accurate results). In one area, the 'green stuff' worked but not in another area I tried. It is for copper and scale stains. Little bubbles formed as it was working which the person at Jack's Magic help line said indicate Calcium stains. He also said that given the low water temp and inconsistent results, he would not recommend using the 'green stuff' stain remover at this water temp as he could not guarantee satisfactory results. I am in a hurry and don't want to wait for the water to warm up. He said another possible treatment is to lower the pH (really low) and brush the pool walls daily. (He recommended adding 12.5 gallons of muriatic acid - in a 25,000 gallon pool) He said that this method could take a week and that twice daily testing for CH would have to been done to ensure that the plaster on the pool walls was not dissolving. He said a spike in CH would indicate a problem, the pool would then have to be 1/2 drained and refilled.
    He said another alternative would be to drain and acid wash the pool.
    I need to try to take care of the stains in the next couple days.
    Any other suggestions? What is the best way to get rid of stains due to calcium deposits?. Last spring after being away, my TA was sky high and I assume this is what caused the Calcium to precipitate out of solution and stain the walls. Does the ascorbic acid treatment work for calcium?
    If I lower the pH and brush, will that help? If so, how low should I go?

    Thanks!
    25,000 gallons
    gunite pool well over 10 years old?
    FAC 0 (deliberatley low to meet stain test kit parameters)
    TAC 0
    CH 275
    TA 60
    pH 7.2
    Temp 55 F
    location TX

  3. Back To Top    #3
    JasonLion's Avatar
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    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: I have dark stains on the surface of my gunite pool

    The only reliable way to remove calcium staining is a drain and manual acid wash. The procedure Jack's recommended works sometimes, takes essentially forever sometimes, and doesn't work at all sometimes.

    Ascorbic acid does not work at all for calcium.

    However, calcium staining is almost never dark/black, usually it is white, green, gray, or brown, with a strong preference for white or off white shades.
    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

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