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Thread: How much chlorine/bleach- too much produces false readings?

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    cfclay's Avatar
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    How much chlorine/bleach- too much produces false readings?

    I've only had my pool open 10 days; I added 182 oz of bleach over 4 days; and added 4 lbs of CYA over two days.
    As I mentioned in a previous post- my FC (through OTO testing)- indicated 2 ppm 24 hours after my last addition of any chemical.

    I added 71 oz of bleach as indicated on the pool calculator to bring FC to 4 PPM.

    24 hours later- it hardly looks like there is any chlorine in my readings.

    I've read on the internet that too much chlorine can actually throw readings off to indicate little or no chlorine in pool

    Having added 250 oz of bleach in ten days- surely this is the case right?

    How much chlorine or bleach do you add daily or weekly under "regular" conditions when you get going?
    Intex 22' x 52" - Intex Krystal Clear Sand Filter Pump - flow rate: 2,150 gal per hour
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    Mod Squad JohnT's Avatar
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    Re: How much chlorine/bleach- too much produces false readings?

    You would normally expect to add enough for 2-3ppm per day, but this is a generalization. For your pool, that would be 71 to 106oz per day. Most likely you need more chlorine.
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    Re: How much chlorine/bleach- too much produces false readings?

    Very high chlorine levels ( above 10ppm ) will skew a PH reading to the high side . With the proper test kit you can measure chlorine to 50ppm or more. Your chemistry is only as acurate as your testing. What test kit do you use?
    Chlorine will be consumed by several sources, sunlight splash out etc. If you can , test your CYA ( stabalizer ) level , provided it has been at least a week since adding it. Your chlorine consumption sounds fairly normal so far.
    coloeb,
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    cfclay's Avatar
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    Re: How much chlorine/bleach- too much produces false readings?

    That range of bleach per day throughout the season? Wow- I didn't realize that. My CYA is about 40
    Intex 22' x 52" - Intex Krystal Clear Sand Filter Pump - flow rate: 2,150 gal per hour
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    Mod Squad Bama Rambler's Avatar
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    Re: How much chlorine/bleach- too much produces false readings?

    If you're using the OTO chlorine test, it doesn't wash out. You may not know how much chlorine you have in there but if there is any it'll change color. The DPD test will wash out above a certain FC level.

    250oz of bleach is almost nothing for a 27' pool over ten days. I use more than that a week in a perfectly balanced pool. Our pool averages 48 oz of bleach per day with a CYA level of 50ppm.
    Dave J. TFP Moderator
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    Re: How much chlorine/bleach- too much produces false readings?

    48 ounces of 6% bleach in 14,660 gallons (24' round x 54") is around 1.6 ppm FC per day which isn't bad, especially for 50 ppm CYA.
    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
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    Re: How much chlorine/bleach- too much produces false readings?

    Quote Originally Posted by cfclay
    I've read on the internet that too much chlorine can actually throw readings off to indicate little or no chlorine in pool
    That can happen with the DPD chlorine test (add drops to the sample to turn it shades of pink, and compare to a color block). The other chlorine tests (OTO and FAS-DPD) don't have that problem.
    --paulr
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