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Thread: Disappearing FC?

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    Disappearing FC?

    So the past weekend I noticed my FC level dropped to zero. I assumed I might have something blooming. Although the water is crystal clear and blue. So I added some liquid chlorine and did an overnight test. It went from about 5.5 to zero overnight. Still completely clear. But I shocked the pool, brought FC up about 20 ppm. Within 8 hours (daytime) it dropped to 8 ppm or so. Brought it back up and it dropped again. I've been battling this for 4 days.

    Although it appears the drop is less pronounced now. Today I started at 20 ppm at about 8am, at 7pm it tested at 14.5 with the salt system on. So it's still losing. Again, the water is crystal clear. There is no sign of green or clouding what so ever. Filter also not dirty.

    I do have a salt system. And my CYA was low...40ppm, which might have explained why it disappeared initially.

    CC was at 2 ppm at the's now testing at 0.5.

    PH, CH, and TA are all within normal range.

    Anyone have ideas where the FC is going? Could this be an ammonia problem?

  2. Back To Top    #2
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Disappearing FC?

    Well, clearly you have something in the water consuming the chlorine, whether it is ammonia or not is irrelevent. Just continue the SLAM process until you pass the 3 criteria to stop.

    Sounds like you caught whatever is going on pretty early since the water stayed clear.
    Jason, TFP Moderator
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  3. Back To Top    #3

    Join Date
    Jun 2012
    Louisville, KY

    Re: Disappearing FC?

    Just sounds like you've got something growing in the water (because you let FC get below minimum). Time to SLAM. When SLAMing it's important to keep that consistent shock level for FC and test frequently, every couple hours if you can. That whole work thing can get in the way.

    It would be a good idea to raise CYA to 70-80 when you're done. Also turn off the SWG when performing a OCLT. You'll probably be done in 2 days because you caught it early.
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

  4. Back To Top    #4
    pwrstrk's Avatar
    Join Date
    Aug 2012
    Elverson Pa.

    Re: Disappearing FC?

    I would turn off SWG all together while SLAMing.

    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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