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Thread: Pool math chlorine question

  1. Back To Top    #1

    Join Date
    Jul 2016
    Valparaiso, IN

    Pool math chlorine question

    When I enter 8% chlorine into the FC table the calculator it reads "Weight", however when I enter 12.5% the word changes to "Trade". Just wondering what the difference is and why that difference is noted?

    Aqua Leader 27' (54") 17,100 gallon, Hayward SW 256T sand filter, Hayward 2 hp 2-speed pump, water testing with a TF-100.

  2. Back To Top    #2
    JoyfulNoise's Avatar
    Join Date
    May 2015
    Tucson, AZ

    Re: Pool math chlorine question

    Bleach sold for laundry use is sold by weight percent of sodium hypochlorite. That's 6% and 8.25%.

    Liquid chlorine sold for pools is typically listed as Trade % which is really a volume %. That covers 10%, 12.5% & 15%.

    The difference between weight and volume percent have to do with the specific gravity of the solution. It changes the FC calculations slightly.
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

  3. Back To Top    #3

    Join Date
    Sep 2016
    North Kansas City, Missouri

    Re: Pool math chlorine question

    That is very helpful, JoyfulNoise. Thank you. I didn't realize that the laundry version was listed as weight %.

    I just got a quote from a chemical supplier for 12.5% Sodium Hypochlorite. 12.5% by weight is 15% by volume.
    Not your typical pool. 130K, in ground pond, 30 mil BTL liner (polyethylene), 3 EasyPro PS10E Eco-Series Ovation Pond Skimmers w/ EasyPro EP9700 Large Mag Drive Pond Pump, Max Flow 9700 Gallons-Per-Hour. Lined with river rock and other rocks. Originally had plants, set up as a natural pond. Kansas City, Missouri. TAYLOR K-2006 TEST KIT COMP CHLORINE FAS-DPD.

  4. Back To Top    #4

    Join Date
    May 2016
    Troy IL

    Re: Pool math chlorine question

    Interesting. So the 8.3% great value bleach at walmart is actually probably a higher percentage of sodium hypochlorite than the 10% liquid chlorine they were selling in the pool section for a while. That would explain why when I switched from the liquid chlorine stuff to the laundry aisle stuff, I didn't have to alter the timing on my stenner to meet my target FC level, even though going from 10% to 8.3% made me think I should have had to use more.

    17,500 gallon IG Vinyl
    Pentair Tagelus TA60D Sand filter
    Pentair Challenger 1.5HP pump CFII N1 1.5A
    Taylor K-2006-A, Stenner 45MPHP10 auto chlorine feed

  5. Back To Top    #5

    Re: Pool math chlorine question

    1.45 oz 8.25% provides the same amount of chlorine as 1.16 oz of 10% or 1 oz of 12.5%.
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