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Thread: Shock Level For CC Buildup

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    Shock Level For CC Buildup

    I noticed from the Pool School that there is a recommended shock level based on the CYA level in the water but elsewhere I have read that the FC shock level is based upon the amount of CC found. I read somewhere and can't remember where now that the FC needs to be 10 times the CC level to release the combined chlorine atoms.

    I'm guessing that the pool school table would always eventually balance itself out as FC used to break up CC levels would keep reducing the FC level until the CC level lowered. As a science major I'm thinking that calculating how much CC you have and bringing up the FC level to ten times the CC level would be the shortest downtime using bleach to shock the pool?

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    RaviePoolGirl's Avatar
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    Re: Shock Level For CC Buildup

    I believe I have read that same information in a book called "Pool Chlorination Facts" by Robert Lowry. "Combined Chlorine X 10 = Breakpoint" I dont recall the book discussing CYA in relation to minimum Chlorine levels.
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    JasonLion's Avatar
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    Re: Shock Level For CC Buildup

    The entire 10 times CC breakpoint story is a myth, not true at all. The history of that is strange, that myth is derived from another myth which was somewhat different and also untrue. It always amazes me that these stories get repeated so often in so may places when they aren't even remotely related to reality. Shock level for your CYA level will break down CC just fine in an outdoor pool, regardless of your CC level. Things are a little more complicated indoors, but even there it still doesn't match up with the way it is portrayed in the breakpoint myth.
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    Re: Shock Level For CC Buildup

    Yeah, that's it the breakpoint.

    I'm totally new and trying to get a handle on things with the new pool we have before I ever get any trouble or unknowns.

    What I find interesting about this breakpoint is mathematically it should never be possible using poolschool's recommended FC target level to get any CC in your pool if you maintain the FC level properly and especially keeping a tight watch after heavy bathing load and/or kids potentially pee peeing in the pool.

    Assuming you start out with a clean slate and CC is zero the moment CC would become measureable, lets say 0.1 ppm or 0.2 ppm, with a CYA level of 30 and FC level of 4 for example purposes you easily have ten times the CC in FC. That .1 or .2 ppm of CC would be oxidized by 1 or 2 ppm of FC still leaving you the 2 FC level remaining.

    What I also didn't see in the pool school is what the maximum recommended FC level for swimming is at each CYA level.

    10 times CC a myth? I don't know it shows up at MSU. http://www.pested.msu.edu/Resources/bul ... 1chap7.pdf

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    JasonLion's Avatar
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    Re: Shock Level For CC Buildup

    If you want to go into the actual science behind the "breakpoint" story, there is a wonderful post here about it.

    It is extremely unusual to see any CC in a properly maintained outdoor pool. The only times it happens are when FC is maintained well below the recommended minimum, and even then it is rare, or when a large amount of ammonia has been added to the pool.

    The Pool Calculator will give your the recommended normal range for FC at each CYA level. Swimming is alright at anything below shock level. And the highest you should normally go under any conditions is mustard algae shock level.
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    Re: Shock Level For CC Buildup

    Thanks Jason I'll check it out. That Breakpoint thing is everywhere!

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