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Thread: Advantages of low CYA?

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    Advantages of low CYA?

    After refilling the pool I've been adding CYA slowly to not overshoot our target of 40. I'm at about 20 right now, why not just stay there? I add about 30 oz of bleach per day to keep my FC at about 4 in anticipation of reaching 40 CYA. Now I'm wondering why not leave it at 20 and go down to 3 FC?
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    JasonLion's Avatar
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    Re: Advantages of low CYA?

    There are two problems with CYA around 20 in an outdoor pool. First you use significantly more total chlorine. The FC level you target is lower, but you need to add more total chlorine to maintain that level. Second, lower CYA levels mean less total chlorine available to deal with exceptional conditions and thus more likelihood of running out of chlorine completely.
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    susa's Avatar
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    Re: Advantages of low CYA?

    FWIW, three(3) family pools run 24/7 using IntelliFlo VF, IC40 and Simpool with Zero CYA during the summer months. No issues with algae and power use is around 112 to 127 watts, similar to a small light bulb. About once a month I swap out a new bottle of acid into the Simpool suction side and test water, rarely making any changes.

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    JasonLion's Avatar
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    Re: Advantages of low CYA?

    susa, Using a SWG and running the pump 24/7 will solve the running out of chlorine problem, however you are using up the SWG cell lifetime far more quickly than you would with CYA.
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    Re: Advantages of low CYA?

    Also, if you have NO CYA in the water, then your active chlorine level is higher than it needs to be. The recommendation of an FC that is 5% of the CYA level for SWCG pools has roughly the same active chlorine level as a pool with only around 0.05 ppm FC with no CYA and I doubt very much that you are able to maintain, let alone measure, that level of chlorine. Remember that CYA doesn't just protect chlorine from breakdown from the UV in sunlight, but it also significantly moderates chlorine's strength.

    The higher active chlorine level in the pools you refer to mean faster oxidation of swimsuits, skin and hair, faster metal corrosion rates, and faster creation of some disinfection by-products such as nitrogen trichloride.
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    Re: Advantages of low CYA?

    Quote Originally Posted by JasonLion View Post
    There are two problems with CYA around 20 in an outdoor pool. First you use significantly more total chlorine. The FC level you target is lower, but you need to add more total chlorine to maintain that level. Second, lower CYA levels mean less total chlorine available to deal with exceptional conditions and thus more likelihood of running out of chlorine completely.
    So does the CYA "give up" the chlorine it's been holding when the FC drops?

    Quote Originally Posted by chem geek View Post
    Also, if you have NO CYA in the water, then your active chlorine level is higher than it needs to be. The recommendation of an FC that is 5% of the CYA level for SWCG pools has roughly the same active chlorine level as a pool with only around 0.05 ppm FC with no CYA and I doubt very much that you are able to maintain, let along measure, that level of chlorine. Remember that CYA doesn't just protect chlorine from breakdown from the UV in sunlight, but it also significantly moderates chlorine's strength.

    The higher active chlorine level in the pools you refer to mean faster oxidation of swimsuits, skin and hair, faster metal corrosion rates, and faster creation of some disinfection by-products such as nitrogen trichloride.
    I was hoping you would show up!

    I guess I'm confused how CYA works and how it interacts with chlorine... (see above, lol) I'll take your guys' word for it, but I'd really like to know how it all works. I get the feeling you know how that is.
    22,000 gallon in-ground kidney-ish shape: 1 HP pump and Triton TR60 sand filter. NEW: Dolphin Nautilus robot! :)

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    Re: Advantages of low CYA?

    CYA holds some percentage of the FC in reserve, the percentage depending on the CYA level. The FC held in reserve is available should the FC level go down, at which point some of it is released to maintain the % held in reserve. CYA protects chlorine from sunlight so that higher CYA levels lose less total chlorine to sunlight even though you increase the FC level to maintain a constant available chlorine level.
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    Re: Advantages of low CYA?

    The chlorine is released from CYA very quickly where if all the unbound chlorine were to instantly vanish, half of the chlorine bound to CYA could be released in 1/4th of a second. So for practical purposes you can think of CYA as maintaining a low active chlorine residual throughout the pool.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Advantages of low CYA?

    Oh... I see. So the CYA basically calls dibs on all the chlorine and whatever is left is available to oxidize stuff and be burned off by the sun. Then the CYA slowly releases its chlorine to keep the FC level constant, until it ultimately runs out as well.

    Pretty neat stuff!
    22,000 gallon in-ground kidney-ish shape: 1 HP pump and Triton TR60 sand filter. NEW: Dolphin Nautilus robot! :)

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