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Thread: SLAM Sequence - Higher FC than expected

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    Join Date
    May 2014
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    Bear, DE
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    4

    SLAM Sequence - Higher FC than expected

    So part-way through a SLAM and got a higher FC reading than I would have expected according to PoolMath and the amount of bleach I put in. I am using TF-100 for testing. One possibility I was thinking is that maybe my pool size is off, although 35,000 should be close. Reason I know is we got a new liner installed last season and used the garden hose to fill -- the time it took to fill supported 35k. And pool store who originally installed it for the previous owners (and replaced the liner) also say 35k.

    Here is the sequence.

    Tested last night around 9pm
    • FC 0
    • pH 7.5
    • TA 170
    • CYA 55


    Based on this, I calc'd a shock value of FC 22 which would require 1161 oz (around 9.5 jugs) of 8.25% bleach. Poured that in and went to bed..

    This morning at 7:15am, FC tested to a reading of 1 using the FAS/DPD with a CC of 0.5 (green had become much lower - lot of progress overnight visually).

    Put in another 9.5 jugs to shock again (lots of scrubbing the walls here) and went out for a bit.

    Tested again at 12:30pm, FC now tested to a reading of 28 with CC still at 0.5. Color had changed to blue, still cloudy although much less so!

    So what worried me was the FC at 28 .. when I had only intended to shock to 22. What else could cause this, beyond my pool size actually being much less than I had previously calculated? I will say it has been quite cloudy today -- it is bright but direct sunlight has only peeked out a few times.

    Thanks!
    35k gallon IG Vinyl, DE Filter 35 sq ft, TF-100 test kit

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    Richard320's Avatar
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    Jan 2010
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    San Dimas, CA (LA County)
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    Re: SLAM Sequence - Higher FC than expected

    Smaller pool, testing error, or the bleach is really fresh and is stronger than the label indicates. Don't sweat it.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Join Date
    May 2014
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    Bear, DE
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    Re: SLAM Sequence - Higher FC than expected

    Cool, thanks for the support!
    35k gallon IG Vinyl, DE Filter 35 sq ft, TF-100 test kit

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    Casey's Avatar
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    Apr 2007
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    SW PA
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    10,157

    Re: SLAM Sequence - Higher FC than expected

    It's only 6ppm out of range... I was thinking you really reamed it with 20ppm more than necessary.
    I'd bet you my bikini you'll never get TFP water from a pool store!

    24' Sharkline Venture De Filter

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    Mod Squad jblizzle's Avatar
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    May 2010
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    Re: SLAM Sequence - Higher FC than expected

    Could be that the pool is smaller than you think (mine was) and/or the bleach is stronger than you think.

    Just keep track of all you chemical additions and you may find a trend that supports a different pool size.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
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