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Thread: A sudden drop in FC: Cause and effect

  1. Back To Top    #1

    Join Date
    Oct 2007
    Valrico, FL

    A sudden drop in FC: Cause and effect

    Thursday evening I tested my pool for chlorine and pH. Normally I see a variation of a few tenths of a ppm change from day to day. However on Thursday I had a drop of almost 1 ppm! This worried me and go me to thinking about why the drop. I then realized that the day before I filled to pool. I fill with tap water, and in my area, tap water usually runs around 3 to 4 ppm of CC.

    So it looks like the CC in the fill water dropped my FC by 1 ppm. I am going to have to remember in the future to add 1 ppm FC when filling the pool.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

  2. Back To Top    #2

    Re: A sudden drop in FC: Cause and effect

    I've read that more and more public water systems are switchingover to Chloramine to treat tap water. Chloramine is chlorine combined with ammonia.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

  3. Back To Top    #3

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: A sudden drop in FC: Cause and effect

    Yes, the 3-4 ppm CC would consume around 1.5 to 2.0 ppm FC (perhaps a little more) as chlorine oxidizes the monochloramine in the tap water.
    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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