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Thread: CYA and FC

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    CYA and FC

    Hi guys. Quick question:

    If my CYA and FC both are tested to be 0 and I added enough Bleach (Per the pool calculator) to raise my FC to 10ppm at evening time, could the 0 CYA mean one day of sunlight might burn all of the FC when I re-test it ~24hrs later?
    Paul - 26'x47" Round AG; 15,610GAL; Hayward EC30 DE Filter, Hayward Power-Flo SP1540. Test Kit: Taylor K-2006

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    Mod Squad JVTrain's Avatar
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    Re: CYA and FC

    Yes. Without CYA, the FC has no protection from UV light from the sun. You could easily lose 10 ppm in 24 hours with no CYA. With no CYA, the half-life of FC is about 45 minutes, meaning you can lose half of your FC in 45 minutes, every 45 minutes. With 30 ppm CYA, the half-life is about 6 hours.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
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    Re: CYA and FC

    Holy cow! Ok, off to Wally I go
    Paul - 26'x47" Round AG; 15,610GAL; Hayward EC30 DE Filter, Hayward Power-Flo SP1540. Test Kit: Taylor K-2006

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    domct203's Avatar
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    Re: CYA and FC

    Quote Originally Posted by RINat615 View Post
    Holy cow! Ok, off to Wally I go
    Welcome to the forum.

    Be be mindful of how much CYA you add, more is not necessarily better when it comes to CYA. In your listed pool volume it takes about 21oz of granular CYA to add 10ppm. Pool math says 63oz for a CYA of 30ppm.

    Do Not pour it into the skimmer, pour it into a clean sock and hang the sock in front of a return, but don't allow it to rest against the pool surface. Some hang the sock from a pool noodle.

    Squeeze the sock often to help the CYA dissolve. Once it is completely dissolved you can check the level in about a day or so.

    Do do you own a proper test kit?

    Dom
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    Mod Squad pooldv's Avatar
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    Re: CYA and FC

    More here on adding chems to your pool, Pool School - Recommended Pool Chemicals
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