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Thread: Swimming near shock levels

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    Whatrymes's Avatar
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    Swimming near shock levels

    OK, I've become more comfortable with understanding and swimming in water that now has, what would have been considered, high chlorine numbers relative to my CYA level. My CYA is at 50 and I maintain my CL level at 4 - 8 ppm. Still get scared sometimes though.

    But another question comes to mind. I've read several times that swimming up to shock level, relative to our CYA level, is fine. So I could be swimming in water that has a ppm reading of 15 - 19 and all should be fine? I would like to know why that is a belief here but in "The Pool Store" world (don't know how else to reference these things) they would shoot me for cruelty to my children swimming at those levels. Keep in mind, if my CYA level was lower, and I was in the pool near shock level, I would still be swimming in a pool with much higher CL numbers than are considered safe by "The World."

    Just would like to understand, Thank you.
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    Re: Swimming near shock levels

    It is fine. I don't do it, but it's fine. But then, it won't stay at that level very long, it is going to want to come down in a hurry.
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    dmanb2b's Avatar
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    Re: Swimming near shock levels

    Most pool stores don't even measure FC above 10ppm and most have no clue how CYA interacts with chlorine. Even at our recommend shock levels, there is less active chlorine in your water if you had 1-3ppm FC and no CYA. The typical pool owner has no clue what CYA does or that they are even supposed to have some. I didn't before I found TFP and Poolforum

    Chem geek has shared this science before and if I quote him from another post regarding TFP recommended levels... an outdoor pool has an FC that is around 10% of the CYA level (roughly 3-6 ppm FC with 40 ppm CYA) which is equivalent to a pool with 0.1 ppm FC and no CYA.
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    Samantha_in_AL's Avatar
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    Re: Swimming near shock levels

    I got in my pool one day while the FC level was 28. It didn't hurt me at all, other than maybe drying my skin out a little bit.
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    Re: Swimming near shock levels

    Pool store also recommend regular shocking and regular use of algaecide. If their recommended levels were sufficient, then they would not need to recommend such things.

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    Whatrymes's Avatar
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    Re: Swimming near shock levels

    I appreciate all the responses but why? Why were we taught high CL levels were unsafe but now they are not? What's the science (layman's level please) behind this?

    Thanks again.
    15 X 30 X 3.6 Ester williams AGP
    10,800 gallons
    Haywood EC40C90 DE filter 1 HP pump
    TF-100 Test Kit

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    Re: Swimming near shock levels

    Quote Originally Posted by Whatrymes
    I appreciate all the responses but why? Why were we taught high CL levels were unsafe but now they are not? What's the science (layman's level please) behind this?

    Thanks again.
    Most of the chlorine is bound to cyanuric acid. The chlorine that is bound to the cyanuric acid does not react to any significant degree. Only the small percentage of chlorine that is not bound to cyanuric acid is reactive. As the reactive chlorine is used up, more of the bound chlorine is released.

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    Re: Swimming near shock levels

    When I was treating a friend's pool for black algae, we took it up to mustard algae shock level or higher when I managed to mis-read the CYA test (polarized sunglasses can affect the test). I managed to sit in some pool water or got my suit wet or something. That level of chlorine is not kind to delicate tissues.
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    Whatrymes's Avatar
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    Re: Swimming near shock levels

    Quote Originally Posted by JamesW
    Quote Originally Posted by Whatrymes
    I appreciate all the responses but why? Why were we taught high CL levels were unsafe but now they are not? What's the science (layman's level please) behind this?

    Thanks again.
    Most of the chlorine is bound to cyanuric acid. The chlorine that is bound to the cyanuric acid does not react to any significant degree. Only the small percentage of chlorine that is not bound to cyanuric acid is reactive. As the reactive chlorine is used up, more of the bound chlorine is released.
    That explains why I am to keep my chlorine between 4 - 8 ppm but that doesn't explain why I can swim up to shock levels which in this case would be up to 20 ppm. Read any other source about proper chemical levels and it's pretty universal: "WAIT after shocking your pool till your CL levels drop below 5 ppm." I'm not questioning TFP's conclusions, I just can't find an explanation why it is SO different.
    15 X 30 X 3.6 Ester williams AGP
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    Re: Swimming near shock levels

    The truth is behind WHY our pools are perfect and the rest of the WORLD struggles to keep their pools as nice as ours, the reason? We trust the science that backs up the results!

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    dmanb2b's Avatar
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    Re: Swimming near shock levels

    Quote Originally Posted by Whatrymes
    I appreciate all the responses but why? Why were we taught high CL levels were unsafe but now they are not? What's the science (layman's level please) behind this?

    Thanks again.
    Here is how Richard had explained it a while back.

    Quote Originally Posted by chem geek
    At usual shock level where the FC is around 40% of the CYA level, this has the same active chlorine (hypochlorous acid) concentration as a pool with 0.6 ppm FC and no CYA (or possibly 1.2 ppm FC with no CYA at 90ºF) which is lower than found in most indoor pools with no CYA. This is not unsafe, but it will likely oxidize swimsuits, skin and hair more rapidly and certainly one should avoid drinking large quantities of pool water (not something one normally does anyway). You basically will experience more of the annoying aspects of typical commercial/public indoor pools except it shouldn't smell as bad since the bather load is so much lower and it's outside in the sun with better air circulation.
    The Pool Industry will always tell you 1-3ppm, to protect the avg pool owner. Even following their advice and not knowing what role CYA plays, the owner could very easly be way above TFP shock level and not even know it...example FC at 3ppm with no CYA in their water.

    All this said...if you keep up with your pool water chemistry, using TFP's non-shock guidelines, you will rarely ever be at shock level. In my personal experience, my pool has only been shocked at pool opening when the water is to cold to swim in anyway
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    Mod Squad Bama Rambler's Avatar
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    Re: Swimming near shock levels

    Spend some time in the Deep End and Chemistry 201 and you'll find enough science as to why it's safe.

    JamesW already gave you a good explanation. The chlorine that's bound to CYA is not reactive and therefore doesn't contribute to oxidation of skin and clothing.
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