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Thread: Yellow spots on vinyl pool bottom

  1. Back To Top    #1

    Join Date
    Oct 2011
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    Yellow spots on vinyl pool bottom

    New here but have been reading up on my problem a bit here and other forums and blogs. This seems like the most knowledgeable so here we go.

    I've read quite a bit and it seems most people feel these are either caused by metals in the water or are biological. I haven't had my water tested at the pool store yet but a quick test strip showed FC was low at .5ppm, ph 7.0, TA 100. These appeared almost out of no where.

    The pool is about 5 years old and I have never had an issue except for occasional mustard algae which was quickly treated and removed. I have not tried the vitamin c test (water is a bit cold to enter).

    Here's my biggest concerned, I have read of 'under the liner molds' that will cause these stains and cannot be removed. Mine are light yellow. From what I've read these under liner molds usually grow in spots that form lines and that's what I have. I have what look like dog footprints starting in my shallow end and traveling almost in a straight line into the deep end...like a dog walked down my pool leaving yellow footprints.

    What am I up against here? Thanks to anyone who has advice.
    8000 gallon outdoor inground vinyl. Sand filter, Hayward 1HP.

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    JasonLion's Avatar
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    Re: Yellow spots on vinyl pool bottom

    A quick easy test for mustard algae/dirt is to try brushing and see if you can brush them off. Both mustard algae and dirt will brush off, metal stains and mold on the other side of the liner won't brush off at all.

    Mold is very unlikely and is almost never yellow. If the stains don't brush off the odds are they are metal stains.

    With FC that low, algae seems likely.
    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

  3. Back To Top    #3

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    Re: Yellow spots on vinyl pool bottom

    Sorry, forgot to mention, they will not brush off. I am familiar with algae and this is not algae...not that I've ever dealt with. They are about 3-4" in diameter and literally go in a straight line from shallow end to deep end in a straight line.

    I am worried about them being underliner since some of what I read stated that under liner mold tends to grow in lines.
    8000 gallon outdoor inground vinyl. Sand filter, Hayward 1HP.

  4. Back To Top    #4

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    Re: Yellow spots on vinyl pool bottom

    Got a picture?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  5. Back To Top    #5

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    Re: Yellow spots on vinyl pool bottom

    I'll post one tomorrow for sure.
    8000 gallon outdoor inground vinyl. Sand filter, Hayward 1HP.

  6. Back To Top    #6

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    Re: Yellow spots on vinyl pool bottom

    Update: So upon finding these stains yesterday I raised the FC to about 5ppm. I went out this morning to photograph the spots and they are gone as quickly as they arrived.

    Now, just to be clear, these were not algae as I brushed them vigorously upon finding them. Has anyone ever encountered this before?
    8000 gallon outdoor inground vinyl. Sand filter, Hayward 1HP.

  7. Back To Top    #7

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    Re: Yellow spots on vinyl pool bottom

    Tannic acid from fallen leaves or acorns will stain a pool and chlorine usually clears it up. That's all I can think of. Glad they went away.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  8. Back To Top    #8

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    Re: Yellow spots on vinyl pool bottom

    ok. Thanks very much. This is quite a nice site here. Glad I found it.
    8000 gallon outdoor inground vinyl. Sand filter, Hayward 1HP.

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