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Thread: BBB for months - sudden CYA drop

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    BBB for months - sudden CYA drop

    Hello. I've been on the BBB train for a few months now. I bought the FAS-DPD test and have been keeping the pool at around 7 FC since my CA was around 60 since i previously used the chlorine pucks. The CA has been at 60 for months.

    My pool's been looking great but the attached hot tub that waterfalls into the pool had some algae so i decided to shock the whole thing and pour the bleach into the hot tub part since its all an enclosed system.

    The night of 5/19 the FC was down to 3.5 and instead of pouring in 1 183 oz jug as i usually do every other night, i put in 3.5 jugs as per the calculator.
    The night of 5/20 - 28.5 FC. Did nothing.
    Got distracted by a broken shoulder over the weekend.
    This morning it was down to 12 so i added 2 jugs as per the pool calculator
    This evening it was at 12 again.

    I tested the CYA just now and according to the FAS-DPD test, I can still see the black circle when the tube's full to the top - practically 0 PPM of CYA!

    What happened? - how did the CYA plummet so much?

    PS the hot tub looks fine now for whatever its worth. But i had planned on waiting until it drops less than .5 FC overnight as instructed. Now I dont know what to do.

    [EDITED BECAUSE I CANNOT READ A TUBE WITH NUMBERS ON IT]

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    JasonLion's Avatar
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    Re: BBB for months - sudden CYA spike

    The CYA test is sensitive to the lighting used when performing the test. It is designed to be done in direct sunlight with the view tube shaded by your body. When doing the test by artificial light it will often read higher than actual.
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    dmanb2b's Avatar
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    Re: BBB for months - sudden CYA spike

    I would double check that CYA reading...if you can see the black dot with tube filled all the way to the top, your CYA is close to Zero.
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

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    Re: BBB for months - sudden CYA spike

    Quote Originally Posted by dmanb2b
    I would double check that CYA reading...if you can see the black dot with tube filled all the way to the top, your CYA is close to Zero.
    OK, yes, good point. So scratch that last bit and replace with:

    "can still see the black circle when the tube's full to the top - practically 0 PPM of CYA!

    What happened? How did the CYA plummet so much?"

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    Re: BBB for months - sudden CYA drop

    So looking around, it seems like shock chlorination can degrade CYA and since i have an autofill and haven't tested in a while (2-3 weeks?) maybe its just been diluted by evaporation and refilling? so to get it back up should i just add stabilizer and get it back to 70?

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    Butterfly's Avatar
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    Re: BBB for months - sudden CYA drop

    Possible leak? Turn off auto fill and do the bucket test to determine if you have a leak.

    Also, before adding any more CYA, pls have someone double-check the CYA test.
    You can take a water sample to the pool store ~cringe~ and see if they confirm.
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    JasonLion's Avatar
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    Re: BBB for months - sudden CYA drop

    You don't lose CYA to evaporation/refilling. You do lose CYA if you have a leak. It is very rare, but you can also sometimes lose CYA if your FC level falls to zero for a couple of days.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    mariane's Avatar
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    Re: BBB for months - sudden CYA drop

    After reading Jason's post, I checked CYA outside in the sunlight. Now instead of 50 in artificial light, it looks more like 30-40 in sunlight.
    Who knew?
    Thanks Jason
    16 x 28 Doughboy Mystic Garden AGP with 7' deep end (used expandable vinyl liner) ~11,800 gals. Deep end main drain. Thru-the-wall skimmer, one return at deep end. Media Master 150# sand filter. Doughboy PowerPak II pump, 1 hp. Pentair MinimaxCH 150m natural gas heater. Polaris 65 when it feels like working . TF-100 test kit. No longer 'pool stored' 5 years and counting. In sunny but fickle metro-Detroit.

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