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Thread: Overnight FC Loss Test

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    sb127's Avatar
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    Overnight FC Loss Test

    This might be a dumb question, but if my CC is measuring zero and pool water is sparkly clear...is there any reason I should do an overnight FC loss test? I assume there could be organics in my pool that the FC is wiping out as fast as it enters the pool and thus not building up CC. Or is that not a realistic thought?
    20,000G Freeform I.G., Pebble Finish, Rock Waterfall, (2) 2.0HP Jandy Pumps - one filtration & one waterfall, Jandy 60 sq. ft. DE filter, In-floor Cleaning, LXI 4000 Gas Heater, Jandy Aqualink controller, LED lighting

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    Re: Overnight FC Loss Test

    It's a good question. We often use these criteria to describe a pool thats in really good condition....

    1. Your pool water is sparkling
    2. Your CC's are .5ppm or less
    3. You can hold your FC overnight without losing more than 1ppm.

    So, you've met two of the three and, theoretically, you need to meet the other one to eliminate the possibility you stated above.

    You could ALMOST do the same thing by calculating your daily chlorine loss. Anything around 1.5 to maybe 3ppm loss would indicate that there are no organics. The overnight FC loss test, however, is the test that absolutely nails it down and leaves no doubt.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    JasonLion's Avatar
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    Re: Overnight FC Loss Test

    If everything is going well, there isn't normally any reason to do an overnight FC loss test. It is normally only done when you think there might be something wrong, or you are shocking the pool.
    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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    sb127's Avatar
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    Re: Overnight FC Loss Test

    Thanks for the advice. That's about what I figured. I may do it tonight just out of sheer curiosity. That and I'm a little test kit happy anyway.

    I'm just getting started, so I'm trying to get a handle on what the daily FC loss is anyway. Based on one day it appears to be 3 ppm. After another few days, I'll have a more solid idea. 3ppm doesn't seem too out of line especially since the pool gets about 8 hours of full Texas sun.
    20,000G Freeform I.G., Pebble Finish, Rock Waterfall, (2) 2.0HP Jandy Pumps - one filtration & one waterfall, Jandy 60 sq. ft. DE filter, In-floor Cleaning, LXI 4000 Gas Heater, Jandy Aqualink controller, LED lighting

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    sb127's Avatar
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    Re: Overnight FC Loss Test

    Bumped my FC up to 6.5 (CYA 50ish) yesterday evening and it held overnight....measured 6.5 FC again this AM. Thanks once again for the info guys.
    20,000G Freeform I.G., Pebble Finish, Rock Waterfall, (2) 2.0HP Jandy Pumps - one filtration & one waterfall, Jandy 60 sq. ft. DE filter, In-floor Cleaning, LXI 4000 Gas Heater, Jandy Aqualink controller, LED lighting

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