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Thread: OCLT passed, pool clear, but little patches of green

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    Prav's Avatar
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    Nov 2010
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    Miami, FL
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    OCLT passed, pool clear, but little patches of green

    Yesterday, my eyes were drawn to some extremely small (<1/16th inch) patches of (dark) green at the tile-line in a couple of corners of the pool. They felt algae-ish (read: slimy) and when I rubbed a puck on them, they seemed to fade. Unfortunately, didn't take pics.

    FC: 6 on Saturday evening; 6 Sunday morning; 5 Sunday evening after full day of sun (added some more, did not test again)
    CC: 0
    pH: 7.6
    CYA: 50
    CH: 380
    ALK: 80
    Borates: 50
    Temp: 87
    Water: Clear (can clearly see main-drain screws)
    Other observations: lots of little debris (bugs, pollen, dirt) in water, but nothing that a little filtration won't take care of.

    OCLT passed (yes, I did remove the puck floater) both last weekend and yesterday.

    So, a few questions:

    (a) In theory, should I have raised CL to shock (20) before I have a valid OCLT? CL is usually in the 7-10 range when I'm paying attention, but likely has been in the 5-10 range due to tax season (done tomorrow!)
    (b) Could it be something other than algae? Copper stain? Would not think that would be slimy to the touch.
    (c) If algae but all numbers appear fine, could it be a circulation/brusing problem? Admittedly, I have not been brushing much lately due to tax season, so it is possible that some of those crevices just have not had good movement to prevent those little things from spouting up.

    As always, thanks much for the feedback!
    14'x30' (est. 14K gal) w/spillover spa (est. 500 gal) - 1995 // Diamond Brite Blue Quartz - 2006
    Hayward SwimPure Plus T-15 - 2013 // Zodiac MX-8 - 2013
    Plain ol' Intermatic mechanical timer // Pump: 1 HP Pentair SuperFlo - 2012
    Filter: Hayward C17502(S) Cartridge Filter - 2011 // Heat Pump: Sunrunner/Aquapro 1300 (127K BTU) - 2011

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    Re: OCLT passed, pool clear, but little patches of green

    Green, slimy, and on the walls almost invariably means algae. Stains aren't slimy. Pollen doesn't accumulate on the walls. I would try brushing it off. If it brushes off (perhaps will a little effort) then it just about has to be algae.

    With CYA around 50 the minimum FC level is 4, so there shouldn't normally have been a problem. Bad circulation is one possibility. Lower FC levels in the past are another possibility.

    It sounds like it is time to shock the pool, with extra attention to brushing throughly.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Feb 2008
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    Denton, TX
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    Re: OCLT passed, pool clear, but little patches of green

    Brushing is really important here because it increases the algae's exposure to the chlorine. Makes the shock process work better.

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    Join Date
    Mar 2011
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    Sunny Central Florida
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    Re: OCLT passed, pool clear, but little patches of green

    Quote Originally Posted by Prav

    (a) In theory, should I have raised CL to shock before I have a valid OCLT?
    I'd like the answer to this as well.
    IG Plaster 20,000gal, attached spa w/ spillover, hayward C12002 cart filter, 1 1/2hp pump w/ polaris 360
    6/16/12 - PH 7.6, FC 6, CC 0, CYA 30, TA 80, Calcium 310

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    Join Date
    Mar 2011
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    Sunny Central Florida
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    Re: OCLT passed, pool clear, but little patches of green

    Bumping to hear opinions on OCLT that is not at shock level.......
    IG Plaster 20,000gal, attached spa w/ spillover, hayward C12002 cart filter, 1 1/2hp pump w/ polaris 360
    6/16/12 - PH 7.6, FC 6, CC 0, CYA 30, TA 80, Calcium 310

  6. Back To Top    #6
    JasonLion's Avatar
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    May 2007
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    Re: OCLT passed, pool clear, but little patches of green

    The OCLT is still valid as long as the FC level is at least 4 or 5.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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