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Thread: How high is too high for FC?

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    How high is too high for FC?

    Hi all. I've got a pool with relatively high CYA. It was 160 when I started, and via water replacement I got it down to 60. I decided to stop there and let my levels drop as I replace water through the season and over winter.

    So, with that acceptable but still high CYA, I'm maintaining a higher FC number than I'd really like to at 7ppm. My previous pool testing experience had me using a basic taylor kit and just making sure FC was somewhere between 3 and 5. We never even looked at CYA level.

    So as I long for the days I can maintain a lower FC level, I'm wondering, how high would you have to take the FC ppm rating before it started to bother your skin and eyes? I know CC is usually the "smell and red eye" culprit, but there's got to be some level at which FC can irritate also. I'm assuming it's well beyond 7ppm though, right?

    Also, at what point am I doing damage to my vinyl liner?

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    PAGirl's Avatar
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    Re: How high is too high for FC?

    Anything under SLAM value is safe. But I don't think you would want to long term. Keeping your FC within the perimeters of the CYA chart Pool School - Chlorine / CYA Chart target will keep algae at bay, as long as you brush regularly. Because some of the chlorine is bound to the CYA, your active chlorine level at a CYA of 60 and FC of 7 is equivalent to a CYA of 30 and an FC of 4.
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    Re: How high is too high for FC?

    Remember that FC is NOT active free chlorine level. The cya will render 99% of your chlorine inert. The recommended levels for a given cya are about equivalent to having .07 ppm with a cya of 0, iirc.
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    Re: How high is too high for FC?

    Though I knew much of my FC was bound by CYA, I guess I figured it was still chlorine and would still count towards irritating skin and or the liner. But if the CYA is making some of it inert, perhaps I was wrong.

    Either way I plan to keep mine at 7ppm unless I have to SLAM again, or if I for any reason replace a bunch of water and my CYA level changes.

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    Mod Squad YippeeSkippy's Avatar
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    Re: How high is too high for FC?

    Good plan
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