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Thread: Muriatic acid made my stain darker

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    Muriatic acid made my stain darker

    Hi,
    I purchased this house a few years ago, and I kept the previous owner's pool guy. He says that it used to be medium-dark gray, but the previous owner had it acid washed to lighten it up. It is now a varigated light gray.

    My pool guy dumped in some copper last summer and it left some dark gray stains on the bottom where it sat. I just drained my pool, and my pool guy poured a watered down muriatic acid on the spots, and on a couple of rust stains. In all instances, I now have deep dark gray stains. Almost black.

    Does anybody know what I can do to get rid of them?

    Thanks in advance,
    Sam
    "There are no bad days, just some better than others"


    18k, Ig Vinyl, 3/4 us motors, Hayward sand filter, quickpure3 ozone generator

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    Mod Squad jblizzle's Avatar
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    Re: Muriatic acid made my stain darker

    Welcome to TFP!!!

    First why did he add copper? I would fire him over that

    I am wondering if maybe the pool was coated in calcium scaling which made the pool look gray, but now that you have put acid on it (did it bubble at all?) you have removed the scale to expose the actual dark plaster again.

    Does the grey part feel rough at all? Is the black smoother?

    What has the pool guy been using to add chlorine?

    A few pictures might help.
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    JasonLion's Avatar
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    Re: Muriatic acid made my stain darker

    Gray/black stains are generally copper, which can be very difficult to remove, though there are some other much less likely possibilities.

    A drain and manual acid wash is the most reliable way to remove copper stains, though there is a multi-step procedure from Jack's Magic that sometimes works and doesn't require draining. One possibility is that your pool guy simply didn't use enough acid. Another is that this is one of the rare cases where black/gray stains aren't copper.
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    gtemkin's Avatar
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    Re: Muriatic acid made my stain darker

    Not sure if this corresponds with your problem but in order to rectify a stain issue in my newly re-plastered colored pool, my pool contractor came over while my wife and I were out of town, emptied the pool, and gave it what he called a light acid wash. I returned from our trip as they were draining out the last bit of their effluent. If you go to the thread on my problem....

    http://www.troublefreepool.com/large...on-t54445.html

    ....you'll see the pool had a medium to light bluish green color. The acid wash made the entire pool a uniform very, very dark green. It was so dark that I couldn't find the location of several known trowel burn marks that were clearly visible when the pool was a light color. However, within 2 days of filling the pool, traditional re-startup, the light color returned, the trowel burns are now visible again, the original stain is gone, the color is somewhat more uniform however I can see telltale light rings around the pool marking various "levels" as if they may have let the effluent pool stand while they paused the sump pump they were using. They used a garden sprayer to apply the "light" acid. I demanded a 25% credit to cover the potential long term effects of the "light" acid wash.

    So from my brief experience, acid wash can make a colored finish much darker.
    21K gal 16' x 40' in-ground pool built 1959, old school with Jacuzzi bronze pump, American Products 24" Sand Filter & Americana Multiport valve, Jandy Lite2 millivolt heater, Coverstar cover, and classic Kreepy Krauly.

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    Re: Muriatic acid made my stain darker

    Wow,
    I did not expect to receive responses so quickly!

    I have attached a photo. The stain doesn't show as dark as it really is because of the clouds being reflected.

    Thanks!

    Sam
    Attached Images Attached Images
    "There are no bad days, just some better than others"


    18k, Ig Vinyl, 3/4 us motors, Hayward sand filter, quickpure3 ozone generator

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    Mod Squad jblizzle's Avatar
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    Re: Muriatic acid made my stain darker

    So what does the pool surface feel like? Is the dark area smoother or is it all about the same?
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    Re: Muriatic acid made my stain darker

    It's all about the same: fairly rough. However, I chose a fairly light spot in a hidden area near the stairs and took a steel brush to a tiny area. The brushed area definitely darkened quickly.
    "There are no bad days, just some better than others"


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    Mod Squad jblizzle's Avatar
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    Re: Muriatic acid made my stain darker

    You could try lowering the water level a bit below the tile and putting a solution of water/muriatic acid on the light areas. If it bubbles/foams, that would confirm that it is indeed calcium scale covering the pool.

    The roughness kind of points to that in my mind.

    EDIT: Posting a good set of test results may help point to the root cause.
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    Re: Muriatic acid made my stain darker

    Thanks! Another question: If it IS calcium scale, is there a way to add scale to the dark areas to make them less noticable?

    **edit** Or should I acid wash the entire pool to remove the scale? **/edit**
    "There are no bad days, just some better than others"


    18k, Ig Vinyl, 3/4 us motors, Hayward sand filter, quickpure3 ozone generator

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    Mod Squad jblizzle's Avatar
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    Re: Muriatic acid made my stain darker

    LOL ... I do not think that adding scale intentionally, thus making the surface rough, is the correct approach.

    You can either go the acid wash approach ... OR ... as some members do, maintain the chemistry appropriately with lower pH and a lot of brushing and eventually the scale should go away (this may take a long time ... like months to years).

    Acid washing does affect the pool surface and may shorten the life of it some.

    Again ... need good test results from one of the recommended kits to suggest a path forward ... assuming it is calcium scale.
    Jason, TFP Moderator
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