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Thread: Mystery substance after draining my pool

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    Join Date
    Jun 2015
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    Victorville, CA
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    Exclamation Mystery substance after draining my pool

    Hello Trouble Free Pool!
    So long story short, I left for vacation and came back to the green lagoon, decided it would be easier to drain and refill than fight the algae. So I drained it about 3/4 until the drains quit sucking water due to airlock in the pool pump. Left it for a couple weeks like that then finally finished draining with a sump pump.
    After all the water was out, I was left with all these little specks all over the deep end where the water sat stagnant.
    They look like someone took a fine point marker and made little dots everywhere, but they're slightly raised and they don't scrape off easily with a fingernail/wire brush. The pool has been empty for about a month now so I'm hoping whatever it is just got dried out and baked in the sun...

    Is this black algae? Is it algae at all or some kind of mineral deposit in the old worn porous plaster?
    I need to know because I'm planning on epoxying my pool in about a week..

    Dropbox link to photos: https://www.dropbox.com/sh/e6eve9oib...C-RN8g7va?dl=0

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    Richard320's Avatar
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    Re: Mystery substance after draining my pool

    Welcome!

    I haven't got a clue. It looks like minerals, but I've never seen dried algae, so I don't know. Whatever it is, I think I'd want to sand blast it off before painting.
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    Mod Squad jblizzle's Avatar
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    Re: Mystery substance after draining my pool

    Welcome to TFP!!!

    I can not look at the pictures right now, but just wanted to point out that we generally do not recommend painting a pool as it is a very temporary solution ... unless you are OK with draining and painting every few years, I would save up for a resurfacing.
    Jason, TFP Moderator
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    duraleigh's Avatar
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    Re: Mystery substance after draining my pool

    +1 on painting. Members report very limited success despite manufacturers claims.

    You pool surface looks like it has scale. Deposits of calcium attach themselves onto your pool walls and floor and (like yours) often become discolored from algae. There is no easy fix....you are gonna have to acid wash it off and further weaken the condition of your plaster.

    If new plaster simply isn't in the future, the paint will probably do just fine for a couple of years and then begin to chalk off. We see it time and time again here on the forum.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Mystery substance after draining my pool

    Quote Originally Posted by jblizzle View Post
    Welcome to TFP!!!

    I can not look at the pictures right now, but just wanted to point out that we generally do not recommend painting a pool as it is a very temporary solution ... unless you are OK with draining and painting every few years, I would save up for a resurfacing.
    I realize that, but I'm moving out of cali in 5 weeks and I dont have the money to do a plaster job. I intend on doing it the "right way" later on..

    Quote Originally Posted by Richard320 View Post
    Welcome!

    I haven't got a clue. It looks like minerals, but I've never seen dried algae, so I don't know. Whatever it is, I think I'd want to sand blast it off before painting.
    Yeah I figured it would have to be removed mechanically if it doesnt come off with the acid/chlorine wash

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