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Thread: Black mystery stains

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    Join Date
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    MS Gulf Coast- Katrina Survivor - BP Hater!
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    Black mystery stains

    I have 2 large and several small ones. The large ones are quarter sized. I must have some small chips in the gelcoat where it starts because it's always the same places. They flare out with water flow. I can spot treat with citric acid and they fade or go away but come back in a month.
    Water is crystal clear. Any ideas?
    fc-6
    cc-0
    ph-7.4
    ta-150
    ch-300 (was at 150)
    cya 40
    borates-30


    15,000 gal Sun Fiberglass, Glass/Lexan/Aluminum Enclosed Room, 1.5 hp Pentair Whisperflow Pump, Triton 100- 600# Sand Filter, Heat Siphon Heat Pump, 3 Dbl. Seats w/8 Jets, Waterfall, 8' Interfab Slide, Pentair SAm Spectrum Amerlite Pool Light, Stenner MHP5 Chlorine Pump, Kreepy Krauly Vacuum, Bleach, 50 ppm Borates, TF 100 Test Kit

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    Mod Squad Bama Rambler's Avatar
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    Re: Black mystery stains

    Those look like stains from exposed metal. Especially given the fact that they always come back in the same places.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Black mystery stains

    Quote Originally Posted by Bama Rambler
    Those look like stains from exposed metal. Especially given the fact that they always come back in the same places.
    Don't know what metal would be in my fiberglass. I have the 2 larger areas and 10-15 very small ones. I figured it was some type of reaction with chems and pin holes through the gel coat. Just not sure what. At least I can get rid of them. I'm going to try a plastic bag on a pole with a very small hole filled with citric acid and hold the hole over the areas. Should work and use much less acid to rid the stain.
    I'm still listening.
    Thanks
    15,000 gal Sun Fiberglass, Glass/Lexan/Aluminum Enclosed Room, 1.5 hp Pentair Whisperflow Pump, Triton 100- 600# Sand Filter, Heat Siphon Heat Pump, 3 Dbl. Seats w/8 Jets, Waterfall, 8' Interfab Slide, Pentair SAm Spectrum Amerlite Pool Light, Stenner MHP5 Chlorine Pump, Kreepy Krauly Vacuum, Bleach, 50 ppm Borates, TF 100 Test Kit

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    Mod Squad Bama Rambler's Avatar
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    Re: Black mystery stains

    Something could have gotten under the gelcoat during mfg but that doesn't seem likely.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    eripaulie's Avatar
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    Jun 2009
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    Metro Detroit, Michigan (30 Miles north of Detroit)
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    Re: Black mystery stains

    I have the same black dots with the flare out "tails" that you do. I have several but they are only as big as the smaller one in your bottom picture. Have never figured out what they are. I have tried to find pictures of what cobalt staining looks like but haven't been successful. They are on the bottom of the pool and the sides. I did try a vitamin c tablet on some on the ones on the sides, they fade for only a moment then reappear. I will be following this thread to see if you come up with anything.
    15,800 gallons
    Sta Rite Cristal Flo Hi Rate Sand Filter Model # T240BP-1
    Inground
    Fiberglass
    1 HP Sta Rite Dura Glass Pump
    Filter and Backwash Flow Rate 63
    Hayward 200000 BTU Heater

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    Re: Black mystery stains

    Most likely to be cobalt staining. Cobalt is used as one of the chemicals in some fiberglass resin. A reducing agent, such as ascorbic acid or oxalic acid might help temporarily, but the stains are likely to reappear. Using a higher calcium level and a sequestrant might help reduce reoccurrences. However, I think that the pool would need to be refinished with a high quality gelcoat to prevent future reoccurrences.

    Of all the raw materials used to manufacture fiberglass pools, gel coat is by far the most expensive per pound. If a manufacturer wants to cut costs, this is a good place to start, because on a brand new pool, ordinary gel coat looks just exactly like the best gel coat that money can buy. But just wait 24 or 36 months and you will see a big difference. Premium gel coat won’t produce water blisters and black cobalt stains, and ordinary gel coat will.


    http://www.sanjuanpoolsok.com/manufacturing-process/

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