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Thread: Black Mold/Algie in Tile grout of Fiberglass pool

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    Black Mold/Algie in Tile grout of Fiberglass pool

    I have had a fiberglass pool for three years now.

    Around the perimeter, at the water line, I have a row of tile. This tile is attached to the pool and grouted in what appears to be white silicon caulking, or some pool friendly version of this.

    I have black mold/algie in the grout/caulking around half the pool, and it seems to be getting worse each year. I have tried a bunch or different cleaning things, including bleach, but nothing seems to help.

    The pool company has been no help.

    Any ideas?
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    Join Date
    Apr 2012
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    Yakima, WA
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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    try soft scrub.
    Dave
    Yakima, WA (the Palm Springs of Washington!)
    IG kidney 14k gal, 33 x 18
    vinyl liner
    200 lb Sand filter
    3/4 HP pump
    First time pool owner

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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    Thanks Dave I will try. The problem is that it is not hard grout, its soft caulk with the mold in it. Almost like mold in a shower.

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    Join Date
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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    That is one of the things we use it for. It has bleach in it.
    Dave
    Yakima, WA (the Palm Springs of Washington!)
    IG kidney 14k gal, 33 x 18
    vinyl liner
    200 lb Sand filter
    3/4 HP pump
    First time pool owner

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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    Is it at, below, or above the waterline most of the time?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    yes, it is at or below the water line, and on the side of the pool that the tile gets shade from the overhang. The water is usually in the middle of the diamond in the picture.

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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    Algae grows in pools that are under-chlorinated. Once established it takes a LOT more chlorine to kill it.

    Here would be my path.

    1. Post a complete set of test results so we can get a picture of your pool water chemistry. Short of that, tell us how you have been chlorinating the pool and how you have tested chlorine levels.

    2. Once you get a very good grip on what's required to get your pool water in shape, be prepared to over chlorinate your pool to kill the algae. I can't say how much that will be until you get us some test results. Secondly, on a daily basis, I would take a stiff bristle brush on a handle and manually scrub the black spots daily. This allows the chlorine to work far more effectively on the algae by exposing it's "innards". (sorry abouyt the redneck description).

    You must plan on this taking some time and diligence and it is conceivable all of the black may not come out. The caulk was the wrong thing to use but your stuck with it for now. Perhaps this method will fix it completely or reduce it enough to make it livable.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    Thanks Dave,
    I am in Boston, so my pool is not even open yet and the water line is just below the tiles.

    I was hoping I could do some scrubbing before it gets open in a couple weeks. Its a salt water pool. I add schock a couple times a year, but other then that I have not had to add anything, the water has stayed clear.

    I will post a water sample in a few weeks. Do you think I can do anything before that to help?

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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    Do you think I can do anything before that to help?
    Well, it's hard to get your water at the proper chemistry when we don't know where it is.

    Since you already applied bleach (as a cleaning solution, I guess) I think the only approach that will work is a longer term dose of bleach in your water.....we just can't effectively suggest what level that will be until you get us your test results. Be sure to include CYA, pH, TA,FC and CH so we get a really good place to start.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Join Date
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    Re: Black Mold/Algie in Tile grout of Fiberglass pool

    I feel it should be mentioned that pool store results and test strips are not going to help much. You will need to buy a good test kit, either the TF-100 or K-2006 from tftestkits.net. It may seem expensive, but in the long run it will save you money and frustration.
    John
    7 year old ~13,500 gal 24' AGP with 1.5 hp Proline pump, 150 sqft Pleatco cartridge, filled with well water with pH of about 4.5.
    Wanda the Whale pool vacuum, home made heater, Taylor K-2006
    Cloudy Pool? 1) Order test kit. 2) Follow SLAM
    New to TFPC? Read Pool School a few times, then post questions. PoolMath will help with chemical additions.

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