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Thread: Why is FC going down so fast?

  1. Back To Top    #1

    Join Date
    Aug 2012
    Location
    Near Sacramento, CA
    Posts
    47

    Why is FC going down so fast?

    I drained and refilled the entire pool a week ago.
    I have been trying to balance the water all week.
    Latest:
    FC 8.0
    CC 0
    pH 7.8
    TA 200
    CH 250
    CYA 40

    I have added acid to bring down the pH over the week when I wasn't shocking with FC >10. It's 0.2 higher today than a few days ago last I checked.
    I added CH and got to 250.
    I added CYA and got to 40 (I even ordered the standard CYA 50 so I could compare and the pool store used the dot with the handle and I looked at that myself. I was so concerned about CYA that I needed to make sure for myself so I'm pretty confident it's 40).
    Starting Friday I shocked the pool at algae levels for over 24 hours - I tested frequently and added when needed and tried to keep FC at 16-17. This morning @7:45AM I thought I passed the OCLT. So today I thought I would stop shocking and see where the FC landed and start to try to keep it at the standard min 3 & target 5 (for CYA 40).
    At 10:00PM FC measured 8.0!! I thought standard loss, even for a direct sunlight pool like mine was around 3-4. Why in the world would my pool lose so much FC? Is that normal?
    The water looks great - it looks better than ever since previously my CH was well over 600 and CYA was way over 100 prior to the drain/fill.
    Thanks for help in advance.
    Outdoor IG Plaster Pool @18,000 gallons
    Cartridge Filter: Jandy CL580 (filter area 580 ft2, Max Flow 150 gpm, 6-hr capacity 54,000g)
    Pool Built est. 2002

  2. Back To Top    #2

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: Why is FC going down so fast?

    During the day you lose chlorine as a percentage, not an absolute number. Your loss rate of 50% is in the ballpark for a CYA of 40 ppm in strong direct sunlight. If you target and start with 6 ppm FC, then you might lose 3 ppm (50%) during the day. If you want to lose less than that, then you may need to raise the CYA level. Anyway, don't worry about the larger loss rate you saw since your FC was high.
    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"

  3. Back To Top    #3

    Join Date
    Aug 2012
    Location
    Near Sacramento, CA
    Posts
    47

    Re: Why is FC going down so fast?

    Hey, thanks so much for the response!! I am feeling way better. Somehow, I must have missed the message that the FC loss would be more of a % than an absolute - which totally makes sense.
    I'm going to continue to work on balancing my water.
    Thanks!
    Outdoor IG Plaster Pool @18,000 gallons
    Cartridge Filter: Jandy CL580 (filter area 580 ft2, Max Flow 150 gpm, 6-hr capacity 54,000g)
    Pool Built est. 2002

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