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Thread: Reason for never-ending algae: pool light?

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    Join Date
    Jul 2011
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    Reason for never-ending algae: pool light?

    My water is clear, but I lose about 2.5-3ppm of FC overnight each night, and I'm adding more bleach than I (think I) should have to.

    I'm generally trying to hold at around FC6 (CYA45), but after a long hot day (it's been over 100 here recently), I can find myself down to 1.5 or 2. At that point, like I've said in another thread, my vinyl seams darken and it appears I'm fighting algae again.

    My pool light was black when I opened earlier this year, but cleared up when the pool did -- after about 55 gallons of 10%. However, now, if my pool gets down to the 1.5FC level, that light starts to blacken right back up. Obviously there's no circulation in or behind the light.

    So, I loosen the light and pull it free; black particulate is flying everywhere, the light housing is rusted and there are holes and water in it (but amazingly, the bulb still works), and the niche (I think that's what it's called) is just covered in black stuff.

    Obviously, replace the light and clean the niche, right? I'm on my fifth paragraph and now getting to my question: how do you do that? I can't lower my water far enough (12" remaining in the shallow end is about 3" above my light) without floating the liner -- do I just use a toilet brush and let the crud go its merry way in the pool water and then rock some "shock+" levels for a while? How do I get the algae that is invariably back in the conduit to the electrical box?

    I want this stuff gone!
    19000 gallon IG installed in 2003, owned by me since 2010, vinyl liner, 18x36, Sta-Rite PLM-150 cartridge filter, 1hp AOSmith motor on <brand unknown> pump, automatic cover, BBB since August 2011

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    Mod Squad woodyp's Avatar
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    Re: Reason for never-ending algae: pool light?

    With CYA of 45-your minimum FC should be 4. Your taget is 3 to 4 points higher than that. Just means you should expect to lose 2 to 3ish of FC per day under NORMAL circumstances. You definitely need to shock with that overnight loss.
    16x32x52" Steel Cornelius Miramar AGP Vinyl liner 13,100 gal. Buried 2 ft.
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    JasonLion's Avatar
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    Re: Reason for never-ending algae: pool light?

    Removing the light fixture for a day while shocking, combined with a little brushing in the niche should take care of it. That will put some debris into the pool, which you will need to vacuum up.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Reason for never-ending algae: pool light?

    Thanks Jason. I haven't been able to find "best practices" on here regarding light/niche maintenance. Should they be removed frequently to avoid this?
    19000 gallon IG installed in 2003, owned by me since 2010, vinyl liner, 18x36, Sta-Rite PLM-150 cartridge filter, 1hp AOSmith motor on <brand unknown> pump, automatic cover, BBB since August 2011

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    Re: Reason for never-ending algae: pool light?

    If you clean it thoroughly enough and maintain chlorine levels, it shouldn't come back. However, we haven't had enough experience of people cleaning behind light niches to know for sure. Those that do so to get rid of yellow/mustard algae don't seem to get the problem again, but you've got something different with that black stuff.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Reason for never-ending algae: pool light?

    This is my exact problem and it is driving me CRAZY! Were your measures successful? Is there a way to rectify this situation without removing the lights? Pool store says they never heard of this problem before and seem like they don't believe me, telling me I should take pictures. The metal ring gets covered in something, too. It doesn't appear too well in pictures.
    Inground Tee Shaped Pool
    Installed 2012
    Approx. 27,000 gallons
    SWG
    Vinyl Liner

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