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Thread: Shadows on the bottom of my pool liner??

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    Shadows on the bottom of my pool liner??

    Hello Everyone – just registered. I’ve got a problem that I hope someone can help me with. I’ve had my in ground pool for 15 years. Two years ago I replaced my liner with a thicker gauge liner and have been happy with it until now.

    Early this summer I noticed what appear to be algae at first, but when I tried to sweep it away it would not disappear. I know its not algae. It continues to expand – more like a shadow or grey (but transparent) stain. It’s only on the bottom of the pool not the walls or the steps. It’s very hard to see on a sunny day but looks terrible on a cloudy day. My chemical levels are perfect. What could it be?

    I just called my installer who has suggested that it is algae growing under the liner. But this liner is an extra thick gauge – I can’t believe algae could seep through!

    Are there any pool owners out there with a similar problem and how can I fix it short of ripping the liner out?

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    24,000 Rectangular Vinyl IG, Sand, 1.5 Hayward Pump

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    Melt In The Sun's Avatar
    Join Date
    Oct 2009
    Tucson, AZ

    Re: Shadows on the bottom of my pool liner??

    Looks like it could be either an organic or metal stain, but we'll need more info to tell (of course )

    Can you post some test results (FC, CC, pH, TA, CH, CYA) and how you obtained them? How are you chlorinating? Do you have well water or an ionizer system?

    I seriously doubt algae under the liner. Based on people's posts I've seen here, "algae or fungus under the liner" has always turned out to be stains on the surface, caused by either metals in the water or more commonly, insufficient chlorine.
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
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    Join Date
    Jul 2009
    Blue Springs, MO

    Re: Shadows on the bottom of my pool liner??

    Is it only along the seam there? It looks darker in the middle right along the seam to me. Could be a leak?
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    Re: Shadows on the bottom of my pool liner??

    ok - I'll have to get the water tested for those metrics. I usually just go by the little Ch /Br / pH measuring kit. Right now those values are 2 / 4 / 7.4 respectively. It's good to hear that you don't think it is under the liner. I couldn't imagine that either. A heavy gauge liner with 30,000 gallons of water pressure all year around? I guess it's possible but I would be rare I think.

    As far as a leak, the picture I supplied was just a small area of the bottom. It is really all over the bottom. It's not solidly miscolored but well distributed - not just on the seams. But I see your point.. thank you.
    24,000 Rectangular Vinyl IG, Sand, 1.5 Hayward Pump

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    Re: Shadows on the bottom of my pool liner??

    Oh - and its just an old fashioned Chlorine pool. I drop a 3 inch chlorine tablet in the skimmer every other day as required to maintain obtimum levels of residual Chlorine.
    24,000 Rectangular Vinyl IG, Sand, 1.5 Hayward Pump

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    Re: Shadows on the bottom of my pool liner??

    More info... two tests are out there regarding stains on the bottom of the pool. Here are the results:

    For Metal stains place a vitamin C tablet on stained area. If it is a metal stain it will remove or reduce the stain. Negative, no change.

    For organic stains place a chlorine tablet on the stain. I was carefull not to let the tablet sit on the liner for more than a minute but guess what - I could see a differnce.

    Assuming this is proof that it is an Organic stain - what's my next step?

    Additional Data - we have had two weeks of 95 - 100+ degree whether here in VA - not sure if that is a factor.
    24,000 Rectangular Vinyl IG, Sand, 1.5 Hayward Pump

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    Join Date
    Feb 2008
    Flower Mound, TX

    Re: Shadows on the bottom of my pool liner??

    Sounds like an organic stain so this calls for more chlorine. You usually don't have to shock assuming that your numbers are okay but simply raising the FC a bit will help it clear.

    What are your test results for FC, CC, CYA, pH, and TA?
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
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    Ashbourne's Avatar
    Join Date
    May 2010
    Western Piedmont, NC

    Re: Shadows on the bottom of my pool liner??

    I had a stain similar to this last year - it went away with each dose of chlorination but it continually came back. Of course, back then I was relying on test strips and some packets of "shock" every few days. No telling what my true levels were...especially CYA.

    I do have a new liner this year but the only other thing that's changed is my management of the pool...accurate testing, the correct CYA and pH levels, and about 3/4 gallon of bleach per day. No stains or any other problems this summer!
    18x36 IG Vinyl, 8.5 deep, 28K, Hayward C4025 SwimClear Filter, Hayward SP2607X10 Super Pump 1HP

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