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Thread: Calibration of some test Issues

  1. Back To Top    #1

    Join Date
    May 2016
    Los Altos, CA

    Calibration of some test Issues

    Are there any expert chemists on this list ? Can you explain how (i.e. the method) to answer the following question:

    How many mL of 8.25% bleach must be added to a 470 us gallon hot tub to make the FC reading go up by 1ppm ?

    If your answer is "I just use pool calculator", that's something I can do too of course, but I'm trying to find an expert chemist.

    Once you know this, you can tell if your test kit is reading correctly or if your bleach strength is low. Knowing this allows you to calibrate some of the test issues you may see.



    Jacuzzi J-375. 470 US gallons. Chlorine.

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

    Re: Calibration of some test Issues

    That's really not the best way to measure bleach as a hot tub can start to consume the FC right away.

    The better way is to do a 10,000:1 dilution with distilled water. Add 10mL of bleach to 1 liter of distilled water and mix thoroughly. Then add 10mL of that solution to another 1 L of distilled water and mix. The ppm's you measure is roughly equal to the bleach strength in % (there's a minor correction to make for "trade percentage" versus "weight percentage " but the answer you get is roughly correct).

    You should use distilled water as it has no chlorine in it and you can get a 10mL metering syringe in the children's medicine section of any pharmacy or on Amazon. If you want to be real precise about it, you can get decent chemical glassware (beakers and graduated cylinders) on Amazon for fairly cheap.
    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

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