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Thread: Help! Pool turned green overnight

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    Help! Pool turned green overnight

    I have had an Aqua Trol on my ag pool for about 3 months and have never had a problem with it. All of a sudden it turned green overnight but you can see through to the bottom and it looks like there may be algea on the bottom

    Here are my levels checked with Taylor K-2006, pool is 16,000 gallons

    FC 8
    CC 0
    PH 7.6-7.8
    TA 90
    CH 220
    CA 70

    Salt reading on the Aqua Trol shows 3000

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    Mod Squad Bama Rambler's Avatar
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    Re: Help! Pool turned green overnight

    Ever used any algaecide in your pool?
    High chlorine will percipitate metals if they're present. And if it's clear but tinted, it may be metals.
    Dave J. TFP Moderator
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    Re: Help! Pool turned green overnight

    No, no algecides have been used. There isn't anything metal in the pool that I know of.

    Quote Originally Posted by Bama Rambler
    Ever used any algaecide in your pool?
    High chlorine will percipitate metals if they're present. And if it's clear but tinted, it may be metals.

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    Re: Help! Pool turned green overnight

    What is the pH? Chlorine can't prevent algae if the pH is out of range.
    25k gal Lazy-L, vinyl liner, poly walls, swimout spa, diving board, TurboTwister slide.
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    Re: Help! Pool turned green overnight

    Sorry, left that one out It's 7.6-7.8? I put one drop of the R-0005 Acid Demand and it brought it down to 7.4

    Quote Originally Posted by MajorDIYer
    What is the pH? Chlorine can't prevent algae if the pH is out of range.

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    Re: Help! Pool turned green overnight

    Quote Originally Posted by MajorDIYer
    What is the pH? Chlorine can't prevent algae if the pH is out of range.
    I don't think PH in or out of range effects the ability of chlorine to kill algae. Would like to hear from the ModSquad on this statement.
    18,500 gallon, 16' x 38' freeform ig plaster w/ 7 ft spill over spa
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    frogabog's Avatar
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    Re: Help! Pool turned green overnight

    Chlorine is more effective at lower pH, that's all. That is one of the reasons to lower pH to 7.2 before you begin shocking. Higher pH levels do not eliminate chlorine's murderous properties, it's just slightly less effective when shocking. For daily maintenance, I do not believe it makes much difference at all.

    7.6-7.7 seems to be my pool's happy place, the chlorine works just as it's supposed to.
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
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    Mod Squad Bama Rambler's Avatar
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    Re: Help! Pool turned green overnight

    Run an OCLT to see if it's really organics. That's the definitive test to determine if you need to shock.
    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
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    Re: Help! Pool turned green overnight

    Higher pH levels do not eliminate chlorine's murderous properties, it's just slightly less effective when shocking. For daily maintenance, I do not believe it makes much difference at all.
    Not too long ago, someone posted that the effectiveness or lack thereof was probably overstated in a previous discussion.

    What I got out of that post was this......chlorine will perform just fine as long as pH is kept somewhere in the 7's as it should be.

    It's (pH) variations within the 7's has almost no effect on the "strength" or "efficiency" of chlorine.
    Dave S.
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    Re: Help! Pool turned green overnight

    Thank you Duraleigh.
    18,500 gallon, 16' x 38' freeform ig plaster w/ 7 ft spill over spa
    Pentair C&C+ 420 cart, Inteliflo 4 x 160 pump - new plaster on 5/5/09

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    Aquatica's Avatar
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    Re: Help! Pool turned green overnight

    how long are you running your pump?

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    Re: Help! Pool turned green overnight

    I tried to find the post where Richard (chemgeek) gave the graphs that show that, with even nominal amounts of CYA in the water the pH effect on chlorine's efficacy is reduced to ~ 0.

    IIRC, it's just another side effect of the chlorine/ cya bond.

    [are you out there, Richard? - I know I'm not explaining this as well as you did ]
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    Re: Help! Pool turned green overnight

    Cyanuric Acid (CYA) acts as an active chlorine buffer. With no CYA in the water, going from a pH of 7.5 to 8.0 cuts the active chlorine (hypochlorous acid) level about in half (50% drop), but with CYA in the water at usual pool levels the active chlorine level drops by about 15% so not very much. The graphs that show this are here. For shocking at higher levels, one can lower the pH first not only to help chlorine, but to reduce the likelihood of metal staining since adding a lot of a hypochlorite source of chlorine raises the pH substantially.

    Now back to the OP's issue. Unless the bottom circulation is very poor in the pool, then what is at the bottom might be yellow pollen against blue vinyl making it look green. On the other hand, as others have noted, a clear green is usually indicative of metal. If you lower the pH (say, to 7.4 or so, not below 7.2) and the color fades, then this is a fairly sure sign of metals. I'd try that first. If you can carefully vacuum-to-waste what is at the bottom of the pool, then you can do that as well (assuming it's dirt or pollen).

    Was your chlorine level always at 8 or is this from a boost in time or shocking you did after you noticed the green?
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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