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Thread: Help! very high combined chlorine

  1. Back To Top    #1
    tacoma5050
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    Help! very high combined chlorine

    What do I do if total Combined Chlorine is VERY high. For example take this current situation:

    I just drained half the water from my pool last week, added new water. Balanced water over the weekend. Then added 3 gals of bleach on Sunday. On Tuesday I added two 1-lb bags of shock. It's a18000 gallon pool with vinyl liner.

    Current readings:
    water is clean, no algee, water is cloudy
    Ph=7.5
    TA=110
    CYA = I think is around 40
    calcium hardness = 120ppm
    FC=.5ppm
    TC= 3.5ppm
    CC=3ppm

    So my breakpoint for shocking is 30. If I use calcium hypochlorite(avail chlor=49%) for shock, a rough estimate tells me I will need 10 to 11 one-lb bags of this shock to reach breakpont.

    That seems like a lot! Is this OK, should I add 10 bags? I have never needed that much shock before. Currently automatic chlorinater has no 3" tabs in it. Should I add tabs and turn it on or wait?

    Will the CC go down on its own after a few days if I do not add any chlorine. I do not care about swimming water is still to cold anyways.

    Also, if shocking with 10 bags of shock is the recommendation, should I lower my ph from 7.4 to 7.2 before I do the shock?

    Also, I have someone recommending that I use a non-chlorine shock, such as a product called "Oxy Shock". They also said I could use a product to remove chlorine from the pool.
    Are either of these good ideas?
    I read in Taylor's "Pool & Spa water chemisrty handbook" that one of the disadvantages of Potassium Monopersulate shocking is that: unlike breakpoint chlorination, it will not remove much combined chlorine. And that is my issue, my CC is very high.

    What is my best coarse of action with my very high levels of these CC?

    Thanks, this is driving me nuts!!!

  2. Back To Top    #2
    JasonLion's Avatar
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    If CYA is really around 40 and this is an outdoor pool then simply bring FC up to 15 and hold it there for a day or two and CC should drop to zero. There are some rare cases where this won't work, but I doubt you will run into one of them.

    Breakpoint chlorination isn't really true the way it is normally explained. In an outdoor pool sunlight helps more reasonable chlorine levels deal with CC in ways that don't work indoors. Even in an indoor pool it isn't really 10x CC that is required.

    The non-chlorine shocks can help but they cost more and chlorine will work just fine so I don't see any point to them (for outdoor pools). Also, some of the common non-chlorine shocks will test as CC, even though they aren't, which can be really disturbing if you don't know what is happening.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  3. Back To Top    #3
    tacoma5050
    Guest
    Quote Originally Posted by JasonLion
    If CYA is really around 40 and this is an outdoor pool then simply bring FC up to 15 and hold it there for a day or two and CC should drop to zero. There are some rare cases where this won't work, but I doubt you will run into one of them.

    Breakpoint chlorination isn't really true the way it is normally explained. In an outdoor pool sunlight helps more reasonable chlorine levels deal with CC in ways that don't work indoors. Even in an indoor pool it isn't really 10x CC that is required.

    The non-chlorine shocks can help but they cost more and chlorine will work just fine so I don't see any point to them (for outdoor pools). Also, some of the common non-chlorine shocks will test as CC, even though they aren't, which can be really disturbing if you don't know what is happening.
    OK Thanks! Yes this is an outdoor pool. I will try bringing the FC up to 15. I will do this by adding 4 gallons of 6% bleach. During this correction period, how often should I check and adjust the FC level, twice a day? (in the morning, then evening).

    I was worried to add more chlorine before I shocked to breakpoint, because I read if you try to shock to breakpoint and you don't use enough shock to reach breakpoint, then you could make matters worse and the CC could raise. So trying to get my FC to 15(as I describe above) and keeping it there for a few days will not increase my CC? I assumed that adding small amounts of chlorine would have the same effect as not shocking with a high enough dose and thus raise my CC.

  4. Back To Top    #4
    JasonLion's Avatar
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    Twice a day will be fine.

    Don't worry about anything the breakpoint people say, it simply doesn't work that way. CC may go up a little right a first, depending on what is in the water, but then it will start going down.

    There are rare cases where the CC is more complex to get rid of, but almost always it is very simple.
    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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