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Thread: why adding chlorine turns water green for 1-2 days?

  1. #1
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    why adding chlorine turns water green for 1-2 days?

    Any thoughts why our pool turns cloudy pea green immediately after adding liquid chlorine or dichlor based shock (2 different brands one with 35% FC, other 65% FC)? After 1-2 days it clears up fine. (Unknown if it clears by filtering or sun baking off the FC). I thought it was minerals/copper from topping off with public well water but today's tests show zero metals present.

    Local pool store wasn't sure as to a solution besides super chlorinating with chlorine free shock (eg potassium monopersulfate) to raise our FC a bit.

    FC 1
    CC 3
    PH 7.6
    T/A 120
    CH 250
    CYA 35
    Metals 0

    Your ideas are appreciated.
    24'x16' Doughboy vinyl AG 10K gal, sand filt, 1.5hp pump, 110gpm approx flow

  2. #2
    Administrator JasonLion's Avatar
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    Re: why adding chlorine turns water green for 1-2 days?

    It is almost certainly metals in the water, either copper or iron. The metals tests are not reliable at fairly low metals levels.

    Adding some sequestrant will clear up the color.

    It is chlorine that causes the color. Using non-chlorine shock won't cause the color change, but it won't prevent it from happening next time.

    By the by, if that CC level of 3 is correct you need to shock the pool.
    [[[EDIT]]]Non-chlorine shock can read as CC, so that is probably where the CC is coming from.[[[/EDIT]]]
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  3. #3
    Mod Squad jblizzle's Avatar
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    Re: why adding chlorine turns water green for 1-2 days?

    Jason was quicker ... my thoughts are the same:

    Well, given you have CC > 0.5ppm. You need to go through the Shocking Your Pool process with good ole liquid chlorine ... don't waste you money on "chlorine-free" shock ... which BTW, cal-hypo is not chlorine-free.
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  4. #4
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    Re: why adding chlorine turns water green for 1-2 days?

    Thanks. Yes, just realized I included cal-hypo by mistake. Ok, sequestrant, wait, more chlorine shock (glad I'm getting the 12% stuff for $2.50gal). I'm getting a handle on this stuff considering I started this year with 200 TA and PH levels from 6.7 to 7.9 and was using Baquacil for the past 3 years.
    24'x16' Doughboy vinyl AG 10K gal, sand filt, 1.5hp pump, 110gpm approx flow

  5. #5
    Mod Squad JohnT's Avatar
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    Re: why adding chlorine turns water green for 1-2 days?

    Quote Originally Posted by Bejay1
    and was using Baquacil for the past 3 years.
    Are you sure you've oxidized all the Baquacil?
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  6. #6
    Senior Member Isaac-1's Avatar
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    Re: why adding chlorine turns water green for 1-2 days?

    I would give the MPS shock about 48 hours to disappear, it can show up as CC on standard FAS-DPD test kits.
    Indoor 20x40 36,000 gallon vinyl pool with 1.5 HP 2 speed Jandy FloPro pump, Hayward EC75 Perflex DE filter, 11 4x12 Techno-Solis panel roof top solar heat with Aquasolar controller, Dolphin Diagnostic Pro Robot Cleaner. Also LMI metering chlorine dispenser pump and soon to be connected UV Ozonator and now Hot Spring Jetsetter standalone spa
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  7. #7
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    Re: why adding chlorine turns water green for 1-2 days?

    Thanks all for the advice. After adding some metal sequestrant the green problem is solved. Two shocks now and water stays clear. Disappointed the testing at our store didn't uncover the true levels present. (Used Malibu brand from American Sale locally - although cheapo at $9/qt it did the job). I'll avoid copper based algicides going forward too.
    24'x16' Doughboy vinyl AG 10K gal, sand filt, 1.5hp pump, 110gpm approx flow

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