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Thread: CYA levels vs chlorine utilization

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    Join Date
    May 2013
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    CYA levels vs chlorine utilization

    I seem to be using a lot of chlorine. The pool has been shocked, stabilized, and my readings are:

    CYA - 50
    pH - 7.6
    CA - 270
    Tot AL - 70
    pool volume - 18,500 gal (in ground plaster)
    Taylor K-2006 test kit

    Every evening I run the chlorine to 5 ppm. By the next afternoon I am down to 2.5 ppm. I am using about 70 oz of 8.25% bleach every day. That will run me about $50/month, quite a bit more $$ than when I was using pool store trichlor or dichlor pucks (if you ignore the cost of changing out the water every so often).

    If I increase the CYA to, say, 70, theory says I will use less chlorine but I will have to go to 5 ppm chlorine to have the same oxidation effect. So, here is my question. Will I really save on chlorine? I'm losing about 50% per day now. What percent will I lose by going to a CYA level of 70? That will allow me to calculate what any savings might be.
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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    JasonLion's Avatar
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    Re: CYA levels vs chlorine utilization

    Yes, the amount of chlorine you will need to add will go down if you increase CYA. The exact amount it will go down by is difficult to predict. Try CYA around 60 first and see what happens.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Mod Squad Bama Rambler's Avatar
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    Re: CYA levels vs chlorine utilization

    You're losing about 2.5 ppm FC per day. That's not bad at all.

    Raising your CYA to about 70 might get you to about a 2 ppm per day loss, but that's about the best you can hope for.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    Smykowski's Avatar
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    Re: CYA levels vs chlorine utilization

    You may have something growing in the pool because you're letting the FC get too low. With CYA at 50, your absolute min hard floor for FC is 4. If you let it get below that you're asking for trouble. You should dose to 7 or 8 and replenish when it gets to 4 or 5. May want to take the chlorine up a bit and run an OCLT to make sure.
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
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    Re: CYA levels vs chlorine utilization

    OCLT did not change overnight, so nothing is growing in the pool. That means my loss is due to UV. Guess I am just looking at about $50/month in bleach costs for the summer at least.
    In-ground plaster pool, ~18,500 gal, Hayward single-speed pump, Pentair 60 sq. ft. DE filter, Polaris 280 robotic cleaner, SPA, heater (seldom used), use Taylor K2006 series test kit

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    Mod Squad Bama Rambler's Avatar
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    Re: CYA levels vs chlorine utilization

    You might try looking around for stronger bleach. Sometimes the pool stores have it cheaper that 8.25% bleach costs.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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