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Thread: Discrepancy between poolcalculator and poolmath for FC shock level

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    Join Date
    May 2014
    Location
    Chandler, AZ
    Posts
    3

    Discrepancy between poolcalculator and poolmath for FC shock level

    I'm a big fan of the TFPC method, but like to use the poolcalculator.com website for calculations (it prints better).

    I have always seen very good agreement between the calculators on both sites, but have found a discrepancy (6 ppm) for the FC shock level. Please see sample values below.

    Is there any way to determine which one is "right"?

    Size: 15900 gallons

    FC: 4.5 now, 9.0 target
    pH: 7.3 now, 7.0 target
    TA: 100 now, 90 target
    CH: 525 now, 525 target
    CYA: 60 now, 60 target
    Salt: 950 now, 950 target
    Borate: 40 now, 40 target

    Temp: 89

    CSI: 0.04 now, 0.29 target

    Suggested FC Levels: SWG=3, Normal= 5-9, Shock= 18 (poolcalculator) 24 (poolmath), Mustard = 34

  2. Back To Top    #2
    Butterfly's Avatar
    Join Date
    May 2007
    Location
    South Carolina
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    10,045

    Re: Discrepancy between poolcalculator and poolmath for FC shock level

    We recommend PoolMath now because we can update it unlike the abandoned poolcalculator. JasonLion (admin here) wrote the software.

    Welcome to TFP
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

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  3. Back To Top    #3

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

    Re: Discrepancy between poolcalculator and poolmath for FC shock level

    The Pool Calculator used shock levels that were a bit lower and more similar to the original Bens' Best Guess Chart, but PoolMath is using the values in the Pool School Chlorine / CYA Chart which for shock levels is roughly an FC that is 40% of the CYA level while for yellow/mustard algae shock level it's roughly an FC that is 60% of the CYA level.

    As for "right", shock level isn't as clear cut as the minimum FC level for algae inhibition (regardless of algae nutrient level) because higher levels kill algae faster. If you go too low when shocking, then there might not be enough chlorine to penetrate established algae clumps fast enough to kill it all off. Using the lower level in The Pool Calculator will probably still work, but may be somewhat slower in bleaching the algae from green to cloudy white.
    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"

  4. Back To Top    #4

    Join Date
    May 2014
    Location
    Chandler, AZ
    Posts
    3

    Re: Discrepancy between poolcalculator and poolmath for FC shock level

    Thanks, chem geek, for the history and details.

    I haven't had to shock / SLAM this year, so keeping my fingers crossed that this is for reference only.
    16K gallon outdoor IG plaster pool with spa overflow (common pump/plumbing) built in 1997.
    Pentair IntelliFlo VS pump, Pentair CCP420 cartridge filter, Pentair MasterTemp 400 NG heater, Zodiac G3 cleaner.
    Using TFPC and TF-100 since 2014 renovation (plaster, tile, deck pavers, equipment).

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