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Thread: Commercial bleach: testing concentration

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    jwfrank's Avatar
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    Commercial bleach: testing concentration

    Is there an easy test for the percent concentration of commercial bleach? I know that over time, bleach will lose some of its chlorine power. Is there a simple test, or calculation using Taylor's kit, that would allow me to test the actual chlorine level of a jug of bleach?

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    Re: Commercial bleach: testing concentration

    Welcome to FTP!

    {EDIT}Corrected an error in the procedure as originally written.{/EDIT}

    There is a way to test the strength of bleach, but it isn't really all that simple. You need to dilute the bleach by 10,000 to 1 and then test the diluted bleach. One way to do the dilution is to add 10 ml of bleach to 1 liter of water, mix throughly, then add 10 ml of that to another liter of water, mix throughly and then test the FC level. The two liters of water need to be chlorine free, commonly distilled water is used. Also, the 10 ml measurement needs to be as accurate as possible, typically done using a syringe or pipette.
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    Re: Commercial bleach: testing concentration

    There is a test for bleach strength. It is usually the iodine/starch titration and is not normally used for pools. Such test kits are available from Taylor Technologies. There are also OTO tests and comparators that go up to 250 ppm from Taylor.

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    Re: Commercial bleach: testing concentration

    The test kit waterbear refers to is the K-1724 from Taylor. It has a resolution of 0.5% Available Chlorine.
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    Re: Commercial bleach: testing concentration

    Quote Originally Posted by chem geek
    The test kit waterbear refers to is the K-1724 from Taylor. It has a resolution of 0.5% Available Chlorine.
    Actually I was referring to the K-1579 which is used to test the strength of bleach with results in % available chlorine and not in ppm chlorine (but it's basically the same test).

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    Re: Commercial bleach: testing concentration

    Ahhh, the K-1579 is a little more expensive, but let's you have a resolution of 0.05% which is a lot better.

    Personally, I just know the strength of chlorine by measuring the FC within an hour of adding it to my pool which has a known size. That's usually good enough to tell me if there is something seriously wrong with the strength of the chlorinating liquid I'm using.
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    Re: Commercial bleach: testing concentration

    Quote Originally Posted by chem geek
    but let's you have a resolution of 0.05% which is a lot better.
    But from a practical standpoint, a resolution of 0.05% requires way too many drops when testing, say, 10% bleach. I use the K-1579 but with a 0.5 mL bleach sample size, 1 drop equals 0.5%.

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    Re: Commercial bleach: testing concentration

    Quote Originally Posted by chem geek

    Personally, I just know the strength of chlorine by measuring the FC within an hour of adding it to my pool which has a known size. That's usually good enough to tell me if there is something seriously wrong with the strength of the chlorinating liquid I'm using.
    EXACTLY!!!

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    Re: Commercial bleach: testing concentration

    Jason, I followed your instructions exactly expecting an answer of "6". (The bleach bottle does state "less than 6%) Taylor K-2006 gave me a reading of .6, not 6. Is this what you would expect from your procedure? being off by a factor of 10 makes me wonder whether we have add too much water. Can you perhaps run through the mathematics of your calculation? Many thanks

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    Re: Commercial bleach: testing concentration

    I am very sorry, I remembered the dilution rule incorrectly.

    If you do 10 ml into 1 liter twice (100 to 1 twice is 10,000 to 1) and then do the FAS-DPD test so that each drop would normally be 0.2 ppm, then each drop is 0.2% bleach (trade percentage).

    Remember that thorough cleaning of the syringe that held full strength bleach is absolutely essential, least there be contamination on the second dilution. Better yet, use a different syringe for each dilution step.

    Keep in mind that trade percentage is slightly higher than weight percentage. Bleach is normally labeled by weight percentage. 6% by weight is 6.17% trade percentage.

    This procedure is an extension of the rule of thumb that adding one gallon of bleach to 10,000 gallons of pool water adds the same # of ppm of chlorine as the percentage of bleach.
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    Re: Commercial bleach: testing concentration

    Thanks, Jason, for clarifying. Stated another way, if I used 1/ 10 the sample based on yr first post (1 ml instead of 10 ml) then the ppm would be 1 /10 as much, which it was: .6 vs 6. So the bleach in the jug was correctly 6% chlorine plus or minus a bit for trade percentage. But certainly in the ballpark of what one would expect. Correct ?

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    Re: Commercial bleach: testing concentration

    If you did what I said the first time, you would have a 1,000,000 to 1 dilution. The correct procedure is a 10,000 to 1 dilution. That is a difference of a factor of 100, so it doesn't account for your results.

    Keep in mind that it only takes a tiny amount of contamination with straight bleach into the second dilution to throw the results off completely.
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    Re: Commercial bleach: testing concentration

    Jason, thanks for the clarification. I went back and retested. Surprising results: bleach contained less than 3 percent free chlorine, using the Taylor kit. The jug's label said "less than 6%" but 3% is quite a bit lower

    Besides having to be much more careful in mixing, splashing, etc, are there major disadvantages to using higher concentrations of 12 % or even 20%? I thought in some posts I had seen warnings against these

    Again, thanks for providing this test info

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    Re: Commercial bleach: testing concentration

    I use 12.5% chlorinating liquid from my pool store as my primary source of chlorine. There is nothing wrong with that except that the chlorine won't last as long as bleach as shown in this table. Since I go through around one gallon per week and get 4 gallons at a time, I haven't noticed any significant loss in strength.

    If you used Clorox Regular unscented, then it should be close to 6%. Also, if you use off-brand "Ultra" unscented bleach, then that is usually close to 6% (though they often have more "excess lye" so result in more of a pH rise over time). It's the off-brand regular bleaches that are often around 3%.

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    Re: Commercial bleach: testing concentration

    Higher concentrations of bleach are fine to use. Their main disadvantage is that their shelf life is substantially shorter than lower concentrations. Oversimplifying a little, 6% bleach has a shelf life of about 6 months, while 12.5% bleach has a shelf life of about 1 month. The highest concentration of bleach I have seen for sale is 18%. It has an extremely short shelf life (a week or two).

    The actual shelf life of bleach depends on the temperature it is stored at, and the purity your supplier provides. Bleach lasts longer at lower temperatures. Actual shelf life can be much shorter or somewhat longer than the times I mentioned above, depending on purity and temperature. As bleach ages it loses concentration, some of the active chlorine breaks down. Old bleach is still usable, it simply doesn't have the concentration you originally paid for.
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    Re: Commercial bleach: testing concentration

    Richard, does the 12.5% chlorinating liquid follow the same rule of thumb that Jason gave earlier:"that adding one gallon of bleach to 10,000 gallons of pool water adds the same # of ppm of chlorine as the percentage of bleach."

    One gallon of this 12.5% liquid would raise a 20,000 gallon pool' s chlorine level by about 6ppm ?

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    Re: Commercial bleach: testing concentration

    Quote Originally Posted by jwfrank
    One gallon of this 12.5% liquid would raise a 20,000 gallon pool' s chlorine level by about 6ppm ?
    Yes, you are correct.
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    Re: Commercial bleach: testing concentration

    When does the clock start running on the shelf life? I am assuming it is from when it was manufactured since most pool users are not going to have an open bottle sitting around for very long. I plan to start using the liquid chlorine this year since what I am hearing on this board that is the best.

    The part of this puzzle I either missed or is not mentioned is how fast it deteriorates. Over a year does it go from 10% to 8% or is it basically bottled water.

    Normally I like to buy a years supply at the start of the season. For me it is a short season. The local superstore starts to put there chemicals out soon after Christmas. I bet their year’s supply of chlorine is already 4-5 months old depending on how quick it got there from the manufacturer. I guess that is why the laundry bleach seems to be the sanitizer of choice.

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    Re: Commercial bleach: testing concentration

    The chart at the bottom of this link might be helpful to you. It gives the half-life (time for losing half the concentration or strength) for chlorine and you can see it is very much a function of concentration and temperature. 6% bleach lasts a long time while 12.5% chlorinating liquid does not last for many months and should be used soon.
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