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Thread: FC Shock Level?

  1. Back To Top    #1

    Join Date
    Mar 2010
    Ridgeway, SC

    FC Shock Level?

    Overnight FC loss from 11.5 to 7..... so, time to shock. If I look at the Chlorine/CYA chart, with my CYA at 80 (about the only thing in my pool where I want it!), it recommends FC to 30ppm (SWCG). However, Pool Calculator, based on my current readings for TA, Borates, CH, CYA calculates 21ppm. I shocked to 21.... do I need to go to the 30 number?

    I have a pretty Irish looking pool now, by the way. Is that to be expected?

    It's exciting to "be in control" of what's in the pool - as opposed to at the mercy of the pool store - but, I'll sure be glad when I get to some level of stability!

    17,000 gal fiberglass. 1.5hp pump, Pentair 60 sf DE filter and Pentair chlorine generator, TF Test Kit, BBB

  2. Back To Top    #2

    Join Date
    Jan 2009
    Cupertino, CA

    Re: FC Shock Level?

    The Pool Calculator and the FC/CYA chart use different methods to arrive at their shock levels. The exact shock level is not critical; anywhere between them will be fine. Pick a target and stick to it, that's the important thing.
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

  3. Back To Top    #3

    In the Industry
    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: FC Shock Level?

    The reccomendations in the pool calc as well as pool school are guidelines. You will do little harm if you stray somewhat from those guidelines so I'd split the difference and set my goal to 25ppm. (21 would work (a little slower), also and 30 would work as well. (perhaps a little faster)

    AS you become more familiar with testing and the parameters, you see that none of the numbers are "set in cement"....i.e. your pool won't go green if FC is 20 or be perfect if FC is 21.

    By far, the most important thing is that you choose a number (say, 25ppm) and then stick with it. Always replenish your chlorine back to that number so the subsequent loss is measurable.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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