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Thread: FC change after chlorine addition

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    Join Date
    May 2016
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    FC change after chlorine addition

    FC 11.5
    CC 0
    TA 110
    CH 290
    CYA 80
    PH 7.6

    Since I have gotten the pool cleared up and looking good with the TFP method, I have been testing everyday to find out how much chlorine the pool needs every day. Eventually, I want to add an automated chlorine system to the pool. I tested last night after dark and found the FC to be 7.5. In order to get to my target FC of 9, the pool calculator said to add 67 oz of 10%. For the first time, I actually measured down to the oz instead of eyeballing it. When I tested this AM before the sun hit the pool, the FC was up to 11.5. Any ideas why this would happen? I messed with the # of gallons on the pool calculator and there would have to be a huge difference in gallons to make a big difference to the amount of FC change from 67 oz of chlorine.
    35,049 gal in ground free form pool, Jandy CL580 Cartridge filter, Jandy SHPF2.0-0 pump, Chlorine

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    Mod Squad woodyp's Avatar
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    Re: FC change after chlorine addition

    Had your pool been circulated well before you tested it at 7.5?
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    Re: FC change after chlorine addition

    Yeah, probably 6 hours worth of filtration. After I added the 67 oz last night, I ran the pump for about an hour on the high speed (2 speed pump). The chlorine was added in the stream of the return jet on the deep end of the pool.
    35,049 gal in ground free form pool, Jandy CL580 Cartridge filter, Jandy SHPF2.0-0 pump, Chlorine

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    Mod Squad pooldv's Avatar
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    Re: FC change after chlorine addition

    There are only a few options
    Testing variability in one of the tests, one of the tests was off
    Strength of the chlorine added, they accidentally put 12% in the bottle or it was really, really fresh
    Amount of chlorine added, you put in more than you thought
    Pool gallons are off, or wrong numbers in Poolmath
    Neighbor snuck over and added some as a prank
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    Re: FC change after chlorine addition

    Looks like the test could have been off....I just retested with the 25ml sample and came up with FC of 8.8- 9.0.
    35,049 gal in ground free form pool, Jandy CL580 Cartridge filter, Jandy SHPF2.0-0 pump, Chlorine

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