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Thread: CYA vs FC sunlight loss relationship

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    Join Date
    Jun 2015
    Location
    AZ
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    CYA vs FC sunlight loss relationship

    Split from original Thread here: CYA vs FC sunlight loss relationship (Mod-Patrick B)

    I'm having the same results. I'm in AZ and the pool is in direct sunlight from 8am - 5pm, pool water is 93.

    Last night I brought my FC up from 3ppm to 9ppm. per the CYA chart.

    Tests from last night:
    FC 9
    CC .5
    PH 8.0
    TA 90
    CH 170
    CYA 70

    This morning all the #'s are the same but FC is down to 8ppm. Pool runs from 7p - 7a.

    I just tested again at 2:30p to see how much I lost and I am down to 4ppm.

    Pool is very clear, no dust on the walls or bottom. Is it typical to add 128oz of 10% liquid chlorine every night. Seems off to me, maybe I need to shock the pool? but with the loss of only 1ppm over night I figured I was ok.

    Thanks
    Chuck
    20000, IG Pebble w/spa, cartridge, k-2006. Fill with soft water

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    borjis's Avatar
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    Aug 2014
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    Pacific NW
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    Re: CYA vs FC sunlight loss relationship

    I'm losing about 3ppm of chlorine each full sun day too but my CYA is 30.

    128oz of 8.25% raises my chlorine 3ppm, so it's a gallon a day in full sun days
    until I raise the CYA a little.
    16x32 IG Vinyl, 13,000 Gals. Hayward S-244T sand filter, SP2810X15 pump
    (1.5 HP motor) Raypak PR266AEN (266k btu) gas heater. TF-100 Test Kit.
    Dolphin E10 Cleaning Robot.

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    Join Date
    Mar 2007
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    San Rafael, CA USA
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    Re: CYA vs FC sunlight loss relationship

    Welcome to TFP, Chuck!

    Your loss overnight if no sun was on the pool is high for normal FC levels. The 1 ppm rule is usually done at SLAM levels. At normal levels the overnight loss is usually substantially less. It would be higher if one had a pool cover since chlorine slowly oxidizes covers.

    Your water is hotter and that will have chlorine react faster so have a higher loss, but there must be something in the water to react with and also the loss during the day is unusually high. Are you sure about the 70 ppm CYA?

    When you checked the loss overnight, was the filter running? If not, try running it and check the loss again. If it's higher, then you may have something in your filter or elsewhere in your circulation path causing chlorine loss. Check your skimmer and pump basket. I assume you don't have an ozonator or UV system as those will consume chlorine.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Texas Splash's Avatar
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    Jun 2014
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    South-Central Texas, Marion/San Antonio
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    Re: CYA vs FC sunlight loss relationship

    Your loss overnight if no sun was on the pool is high for normal FC levels. The 1 ppm rule is usually done at SLAM levels. At normal levels the overnight loss is usually substantially less.
    Well, I just learned something new.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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