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Thread: Does CYA reduce the effectivness of Chlorine as an Oxidizer?

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    pinguy's Avatar
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    Does CYA reduce the effectivness of Chlorine as an Oxidizer?

    I have a tiny (140 gallon) hot tub that uses a Silver Ion sanitation system (explained by chemgeek here).

    The silver needs an oxidizer to work correctly, and the manual instructs weekly additions of Dichlor -or- MPS. They specifically say the use of liquid chlorine will not work with the Silver system properly. I've been using Di-Chlor because it's what I have on hand, but as you can imagine it has increased the CYA level to 100+. So, does that high CYA level change the oxidation properties of FC in addition to sanitation?

    I'm asking more out of curiosity than anything else - the tub is so small it's not a problem to replace a bit of water or use MPS exclusively.
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    Re: Does CYA reduce the effectivness of Chlorine as an Oxidizer?

    Yes, it affects the oxidation as well as sanitation properties of chlorine.

    Why would liquid chlorine not work with the silver system? You can absolutely use the dichlor then bleach method in a tub that also uses silver. I think the point of using silver though is to use MPS and have a chlorine-free tub though, so if you are using the proper amount of chlorine then the silver is kind of redundant.
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    Re: Does CYA reduce the effectivness of Chlorine as an Oxidizer?

    Quote Originally Posted by Donldson View Post
    Yes, it affects the oxidation as well as sanitation properties of chlorine.

    Why would liquid chlorine not work with the silver system? You can absolutely use the dichlor then bleach method in a tub that also uses silver. I think the point of using silver though is to use MPS and have a chlorine-free tub though, so if you are using the proper amount of chlorine then the silver is kind of redundant.
    I'm not sure, it might be manufacturer voodoo. Here is what the manual (and warranty) say:



    For me the purpose of the silver sanitation is so I can add chemicals weekly instead of daily. I think I'll grab some MPS and go chlorine free though - for the smell if nothing else.
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    Re: Does CYA reduce the effectivness of Chlorine as an Oxidizer?

    Just be aware that MPS will show up as CC on the common chlorine tests
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    Re: Does CYA reduce the effectivness of Chlorine as an Oxidizer?

    They are probably afraid that the exclusive use of liquid chlorine will result in problems since it would be completely unbuffered. Since your spa has stabilizer in it using liquid chlorine won't harm anything. Using the silver and MPS strategy is acceptable in a spa, heck it is even FDA approved. Despite the manual my recommendation is to use MPS after a soak to take care of all the sweat and skin and stuff that gets in the water, and then do a weekly liquid chlorine addition to kill off anything that might be lingering.
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    Re: Does CYA reduce the effectivness of Chlorine as an Oxidizer?

    Quote Originally Posted by Donldson View Post
    Despite the manual my recommendation is to use MPS after a soak to take care of all the sweat and skin and stuff that gets in the water, and then do a weekly liquid chlorine addition to kill off anything that might be lingering.
    The manual says MPS instead of di-chlor is fine, which I'll do when I refill. I just wasn't sure if the CYA affected oxidation, as the manual does not mention CYA anywhere.

    Am I correct in assuming CYA has no affect on MPS as an oxidizer?
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    Re: Does CYA reduce the effectivness of Chlorine as an Oxidizer?

    Quote Originally Posted by pinguy View Post
    The manual says MPS instead of di-chlor is fine, which I'll do when I refill. I just wasn't sure if the CYA affected oxidation, as the manual does not mention CYA anywhere.

    Am I correct in assuming CYA has no affect on MPS as an oxidizer?
    MPS will not be affected by CYA. CYA reduces the oxidation rate of chlorine because it lowers the concentration of HOCl/OCl- in the water. Oxidation reaction rates (like many chemical reactions) are 1st order reactions, i.e., rate is proportional to the concentration of reactants and products. So, if you lower the concentration of HOCl, then you slow the reaction rate.
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