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Thread: Bright stains on the bottom of a gunite pool

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    Bright stains on the bottom of a gunite pool

    Greetings everyone,

    I'm new to the forums (so please excuse me if I screw something up) and I'm also new to pool ownership. I have a 7,000 gallon gunite pool that's approximately 2 years old (though I have not owned it very long). The pool has been under the care of a local pool company. Recently, I left town for 6 days and upon my return, I found these stains on the bottom of the pool:

    Pool_Stains_01.jpg Pool_Stains_02.jpg Pool_Stains_03.jpg Pool_Stains_04.jpg

    The pool looked beautiful and blemish free before I left town. What do you think could have caused stains like this?

    Thanks in advance for your experienced opinions/thoughts!

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    Mod Squad pooldv's Avatar
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    Re: Bright stains on the bottom of a gunite pool

    Welcome to TFP!

    My guess is calcium scale. Pool School - Calcium Scaling

    Posting some test results will help determine if scale is likely. Are the stains rough? Raised?
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    Re: Bright stains on the bottom of a gunite pool

    Thanks for the response pooldv, and for the link. Could calcium scaling have happened so quickly - in just a few days? The stains were not rough - they were the same smoothness as the rest of the pool. Also, I forgot to mention that there were no stains on the walls of the pool, only on horizontal surfaces - like something settled.

    Looking at the service reports from the pool company, prior to stains, they reported 3.0 free chlorine, 3.0 total chlorine, 110 total alkalinity, and 7.8 PH. After stains, they reported 1.0 free chlorine, 1.0 total chlorine, 100 total alkalinity, and 7.8 PH.

    One of the pool guys I spoke with said "someone screwed up" and mentioned di-chlor as the culprit. Do you think that's possible given the look of these stains?

    Thanks again for your response.

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    Re: Bright stains on the bottom of a gunite pool

    di-chlor is more then likely what caused that especially on a Tahoe blue plaster see it all the time they would have had to use a lot of di-chlor though...
    David Randolph
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    Mod Squad pooldv's Avatar
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    Re: Bright stains on the bottom of a gunite pool

    Yes, if they are smooth then it is certainly possible that dichlor sat on the bottom and bleached the pigment out of the plaster.
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    Re: Bright stains on the bottom of a gunite pool

    That sure looks like a spill that was allowed to stay on the pool surface. There is more than one thing that could cause that but di-chlor would be a good guess.
    Dave S. - Forum owner
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    Re: Bright stains on the bottom of a gunite pool

    Were they trying to treat algae or something ?

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    Re: Bright stains on the bottom of a gunite pool

    I was going to ask about that, but it looked like a widespread area from the picture. Is it all in one area, or all over?
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    Re: Bright stains on the bottom of a gunite pool

    Thank you all for the replies. I'm not sure if they were trying to treat algae. I did notice in the notes that just prior to this staining, they added "3 lbs Cal Hypo Shock 1 lb Tabs".

    PAGirl, this image shows the shallow end of the pool and you can see the staining on the steps and across the bottom of the pool. The other end of the pool has the 2 intakes pictured above.

    IMG_4751.jpg

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    Re: Bright stains on the bottom of a gunite pool

    Cal Hyp 1" tabs are a poor choices for pool applications. Someone doesn't know what they are doing and should be liable.
    Dave S. - Forum owner
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    Re: Bright stains on the bottom of a gunite pool

    A granular chlorine is a very likely cause. Probably not dichlor as that dissolves fairly quickly. Calcium hypochlorite is the most likely cause. Granular trichlor is the second most likely cause.
    Quote Originally Posted by Swimmingly View Post
    I did notice in the notes that just prior to this staining, they added "3 lbs Cal Hypo Shock 1 lb Tabs".
    They probably meant 1 lb bags, not tabs.

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    Re: Bright stains on the bottom of a gunite pool

    Sorry, I should have separated the "3 lb Cal Hypo Shock" and the "1 lb Tabs" as they were written on separate lines. I'm thinking "Tabs" is referring to the bucket of 1 lb chlorine tablets they sold me when I bought the house. Does that sound right?

    Thanks guys for the info on the cal hypo. I really appreciate your time and responses. I hired the pool company to take care of the pool while I was traveling (and learning about pool care). I never dreamed this would happen while in their care.

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