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Thread: Light brown blotches on white plaster pool

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    Light brown blotches on white plaster pool

    Greetings. Finally time to drain and refill pool. However once drained I notices light brown blotches all over the pool that we never noticed when the pool was full. Any idea what they might be? Pool was replastered about 25 years ago and has been acid washed once. My son and I are planning on acid washing with a 3 to 1 solution this weekend to remove the few light blue copper stains. thanks
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    16 x 36; >45 yrs old IG Anthony pool; 25,000 gallons; Intelliflo variable speed pump; 60 sq in cartridge filter; Pentair Mastertemp pool heater

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    Re: Light brown blotches on white plaster pool

    I'm going to preface this by saying that I know very little about this.

    I will say, however, that I'd be careful with that plaster. Mine is about 18 years old, and I'd do everything I could just to leave it alone to prevent doing something that might force a full replaster in short order. If you don't notice it when the pool is full, personally, I'd just refill the pool and go on with life. Old plaster can be delicate, and leaving it dry in the heat right now is probably not a great idea either.
    8,500gal plaster in-ground with attached spa, two floor drains, one skimmer. Chlorine, City Water.
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    Re: Light brown blotches on white plaster pool

    Are those spots raised and rough? Of so then they are calcium scale. 3 options for that

    Drain and acid wash. Very aggressive, removes plaster and shortens the life of the plaster.

    No drain acid bath, less aggressive. Here's how, The Zero Alkalinity Acid Treatment

    Or you can put some dry acid in a sock and treat specific spots to dissolve the scale.

    Or you can fill it up, lower the CSI to -0.8 to -0.9 and brush as often as you can and slowly get rid of the scale without hurting the plaster much. Use a stainless steel brush to help.

    Then keep keep CSI- 0.3 to 0 to prevent scaling in the future. PoolMath will give you the number, tweak pH and TA to adjust it.

    More here, Pool School - Calcium Scaling
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    Re: Light brown blotches on white plaster pool

    Brown spots are not raised and are smooth.
    16 x 36; >45 yrs old IG Anthony pool; 25,000 gallons; Intelliflo variable speed pump; 60 sq in cartridge filter; Pentair Mastertemp pool heater

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    Re: Light brown blotches on white plaster pool

    Brown spots turned lighter upon 3:1 acid washing.
    16 x 36; >45 yrs old IG Anthony pool; 25,000 gallons; Intelliflo variable speed pump; 60 sq in cartridge filter; Pentair Mastertemp pool heater

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    borjis's Avatar
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    Re: Light brown blotches on white plaster pool

    could it be iron stains?
    16x32 IG Vinyl, 13,000 Gals. Hayward S-244T sand filter, SP2810X15 pump
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    Re: Light brown blotches on white plaster pool

    I think the top surface of your plaster is gone in the brown areas. Don't know what else it could be.

    It's past it's expected life and any acid treatment will make it worse. Any chlorine treatment will not make it worse but it will certainly not make it better.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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