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Thread: Do you absolutely HAVE to shock if FC drops to zero?

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    lka674's Avatar
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    Jul 2012
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    Williamson County, Texas
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    Do you absolutely HAVE to shock if FC drops to zero?

    FC = 0
    CC = 0
    TC = 0
    pH = 7.8
    TA = 60
    CYA = 30
    CH = 450 (I manage by trying to keep the CSI below 0)

    So, my husband and I differ sometimes on our pool philosophy. He believes it's a good idea to periodically shock regardless of testing results. I've always been of the idea that if you don't need to do it...don't. Here's where I'm a little unsure. We went out of town and stayed a day longer than we thought and during that day (based upon a 1ppm FC loss nightly) our chlorine dropped to 0.

    Do you think I absolutely need to shock it? The pool still looks crystal clear and there aren't any chloramines.....I've been told to always shock if it drops to zero, and my DH is telling me to do it now, but there's a part of me that says it may not truly be necessary b/c it was 0 for barely an entire day and all the other numbers check. I was considering just adding chlorine to bring me up to max target range rather than all out shocking.

    Anyone's thoughts on this??
    Pool grand opening Sept 2010. 100% sun exposure. Beach entry with fountain, IG gunite pool, approx 11,000g. Hayward HK sand filter. Intelliflow VS 350 pump w/ max flow rate 160 gpm. Dolphin (cordless) M5 Liberty pool cleaner. The pool has waterfall at one end with a tanning ledge and a spa at the other end that has a spillway into the pool and there is a water shear falling from the pool equip wall into the spa. DH did a beautiful job of designing it himself!

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    Re: Do you absolutely HAVE to shock if FC drops to zero?

    There is no point in shocking unless there is some specific reason to shock. FC falling to zero is such a reason.

    The odds are better than 50% that you don't have to shock the pool right now. But if you are unlucky you are making a lot of extra work for yourself. It is quite possible that something has started growing in the water, even if it is clear right now, and it is better to wipe it out completely and be sure than to play chicken and hope you get lucky.
    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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    lka674's Avatar
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    Jul 2012
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    Williamson County, Texas
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    Re: Do you absolutely HAVE to shock if FC drops to zero?

    Thanks Jason! That's what I ended up doing...I would rather do it and get it over with than spend hours trying to kill algae! Have a great weekend.
    Pool grand opening Sept 2010. 100% sun exposure. Beach entry with fountain, IG gunite pool, approx 11,000g. Hayward HK sand filter. Intelliflow VS 350 pump w/ max flow rate 160 gpm. Dolphin (cordless) M5 Liberty pool cleaner. The pool has waterfall at one end with a tanning ledge and a spa at the other end that has a spillway into the pool and there is a water shear falling from the pool equip wall into the spa. DH did a beautiful job of designing it himself!

  4. Back To Top    #4

    Re: Do you absolutely HAVE to shock if FC drops to zero?

    by the way shocking as defined by TFP is a process not a product you add. (i.e. is your husband saying to add a product called shock?)

    Shocking consists of taking the Fc levels to the shock level for your CYA, then keeping it there until your FC drops less than 1 overnight, pool is clear and CC is <.5


    pool-school/shocking_your_pool
    17,800 gallon, IG pool, 595 sq feet (17x35x4.5 avg rectangle), Hayward 525 cartridge filter, diamondbrite, 2 hp 2 speed hayward tristar filter, Stenner 45mhp10 automatically chlorinating

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