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Thread: Black (or at least very dark) 1/3 ring around my main drain

  1. Back To Top    #1

    Join Date
    Jul 2007
    Location
    Indiana
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    57

    Black (or at least very dark) 1/3 ring around my main drain

    Hello experts,

    First let me say how happy I am to finally be able to log in to a pool forum, I've been interested for a long while and kept checking the "Pool Solutions Forum" site. I first stumbled on to it about 5 minutes after it was locked from any new members.

    I have a 14' x 28' inground vinyl lined pool.

    My pool is about 4 years old. Sometime in the 2nd year I started seeing a dark stain appearing around the main drain. The stain goes about 1/3 the way around the drain and about 2 inches out from the drain, on the deep end side of the drain. I noticed it seemed to fade some when I shocked and returned after as the higher chlorine level subsided. In the middle of the season in the third year the stain started to get bigger, about 1/2 way around the drain and 6 inches out.

    I called the builder to come have look, they thought it was black mold. They had me drain the pool, then they came out and put on a new main drain gasket, mixed up some bleach and muratic acid directly on the stain, let it sizzle for 10 or 15 seconds and then started filling the pool from the water truck.

    This cleaned most of the stain, there was still a tinge of brown, but a lot better. Now, a year later the stain is back to where it was at year two (1/3 the way around and 2" out), doesn't seem to be getting any bigger than that so far...

    Does anyone disagree with the black mold diagnosis? Any thoughts as to why it's only on one side of the drain?
    This detracts from the clean pool I try maintain.

    Thanks
    14'x28' in ground with vinyl liner and a new sand filter (2015).

  2. Back To Top    #2
    Mod Squad JohnT's Avatar
    Join Date
    Apr 2007
    Location
    SW Indiana
    Posts
    8,618
    Welcome to the forum!

    It sounds like mold, but I've never herd of it being is such a localized area. Very little can be done about it without removing the liner, as it's on the back side and just shows through. You might look into one of the drain rings that is designed to help automatic cleaners go over the main drain. It might hide some of it from view.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

  3. Back To Top    #3

    Join Date
    Jul 2007
    Location
    Indiana
    Posts
    57
    Thanks!

    I'll take look at those, guess if there's really not much to be done about it, then hide it!
    14'x28' in ground with vinyl liner and a new sand filter (2015).

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