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Thread: How O need the OCLT be?

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    Join Date
    Jul 2015
    Location
    Rochester, NY
    Posts
    41

    How O need the OCLT be?

    I just started a new SLAM because I suspected Algae.

    Relevant stats are:
    Pre SLAM PH: 7.4
    CYA: a bit less than 40
    FC: 16

    I got too busy working on renovation stuff and just got to testing my water at 1:20 AM (I had added one more FC on a hunch at 9:00PM which got me right on the money for 16 at this test).

    Sunrise is officially at 5:33 AM here, but the pool is west of the house, so it is a bit in the shade at first. If I measure FC at 6:30 or 7:00, is that long enough that less than 1 FC loss is significant enough, or is that too short? Right around the solstice and in upstate New York there isn't a lot of night to do this test.

    I read a couple of other threads I found searching for OCLT threads but I didn't find anything that said less than 1FC in x sunless hours is the good spot. Also worth noting: No bathers today, but lots of dead bugs, leaves, and general tree junk in the pool. Other relevant details if anyone wants to know: I used my brush head vacuum on the whole pool after I got the shock levels up earlier in the afternoon, so everything was stirred and sucked into the filter. I also added some more DE. Oddly, after a while my filter pressure dropped (It went from 14 to 15 after I added DE, then went up to 17, and after a few hours back to 15). And after I connected my vacuum and turned on the pump my return spewed out a cloud of dark stuff, no idea what that was about.

    Thanks for the help.
    24' round above ground 52" vinyl pool - 12690 gallons at 45'' fill.
    Hayward Power-Flo Matrix SP1510Z1XEHC (1HP, SP).
    Hayward S180T 150lb Sand Filter.

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    cowboycasey's Avatar
    Join Date
    Jul 2013
    Location
    Fletcher, OK
    Posts
    3,346

    Re: How O need the OCLT be?

    about 6 to 8 hours of no sunlight, no CC, no loss or less than 1ppm FC and clear water
    Pool: Intex 16x32 15000 gal, 2 speed 340042, Pentair CC320 Filter, CircuPool SJ45 Salt System, Intermatic PE653RC; Hot Tub: 650 Gal SWG Megachlor
    links: pool school * Recommended-Levels * SLAM * CYA chart * Test kits * How To Post Pictures * Poolmath * OCLT ** Support your website if we helped you :) **

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    Join Date
    Jul 2015
    Location
    Rochester, NY
    Posts
    41

    Re: How O need the OCLT be?

    Great, thank you. I just did the test (been 6 hours, and no direct sunlight) and I got 17 FC and >0.5 CC, clear water.

    I've never before tested higher FC on a subsequent test (I made sure to get the water from the same spot), but I guess my water wasn't mixed enough last night. Still, I don't think I would have been off by more than 2.5 FC as I had not put enough chlorine in the pool to even get to 18.5 FC, so I'll assume I passed. That was the shortest Slam ever, I guess.
    24' round above ground 52" vinyl pool - 12690 gallons at 45'' fill.
    Hayward Power-Flo Matrix SP1510Z1XEHC (1HP, SP).
    Hayward S180T 150lb Sand Filter.

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