Info from Clorox on using their bleach for pools

Since I am now injecting a bleach solution with a pump I test every batch I mix up. Today I over-shot on the pumping rate so I decided to mix a weaker concentration. I put one 182 oz bottle of Clorox with two 182 oz bottles of pool water to make what I would have thought to be a ~2% solution. When I tested it ---- it was 3.2% ---- repeated the FAS-DPD test and got the same thing???????:confused: ??????? I did not test the bleach before I mixed it.:mad:

My pool water was 7.3ppm but that's a long way from the 6% ?? bleach that it was mixed with.

Your 3.2% one-third diluted measurement doesn't make sense, even for Clorox Ultra. I don't know what to say. Perhaps try diluting it directly next time. And you are right that your pool water should have minimal effect on the final measurement since it is has so much lower chlorine level than the 6% bleach.

I tested bleach and my injection solution again today and found the Clorox Ultra I bought from Sams is running about 7.2% by FAS-DPD test. What I can't figure is that a 1 to 3 (bleach to water) dilution is still testing at 2.4% solution for my injection pump. Does this compute??? (maybe it's this "new math";) )

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Originally Posted by fcfrey

I tested bleach and my injection solution again today and found the Clorox Ultra I bought from Sams is running about 7.2% by FAS-DPD test. What I can't figure is that a 1 to 3 (bleach to water) dilution is still testing at 2.4% solution for my injection pump. Does this compute??? (maybe it's this "new math";) )

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Well 2.4% is a lot closer than the 3.2% you reported earlier. When you say "1 to 3" do you mean 1 volume of bleach in 3 volumes of water or do you mean 1 volume of bleach into 3 total volumes (i.e. 2 volumes of water)? You are right that starting with 7.2% and truly diluting 1 part plus 3 parts water (a 25% dilution) should yield 1.8% and not the 2.4% you are getting. On the other hand, if you were doing 1 part into 3 total (so 1 chlorine and 2 water), then this would be a one-third diultion which should get 2.4% which is exactly what you got. So either there is something really screwy or your 1 to 3 wasn't 1 part bleach and 3 parts water, but was 1 part bleach into 3 total parts (2 parts water).

Perhaps if you explain how you did the 1 to 3 dilution this might clear things up.

Richard

Aren't these home-brewed tests of chlorine strength hopelessly inaccurate? Aren't the errors inherent in diluting a sample to this level simply huge?

We tell people to dilute water samples by 3 or 4 to 1 so they can test higher chlorine levels with an OTO test but then warn them that the results are just ballpark. Now people are diluting chlorine samples by 20,000 to 1 (or so) and talking about tenths of a percent precision? I dunno...

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Originally Posted by KurtV

Aren't these home-brewed tests of chlorine strength hopelessly inaccurate? Aren't the errors inherent in diluting a sample to this level simply huge?

We tell people to dilute water samples by 3 or 4 to 1 so they can test higher chlorine levels with an OTO test but then warn them that the results are just ballpark. Now people are diluting chlorine samples by 20,000 to 1 (or so) and talking about tenths of a percent precision? I dunno...

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You are right that unless one uses a calibrated pipette, the errors will be quite large. However, having a large dilution ratio does not contribute to the error. An error in a ratio, which is what a 20,000 to 1 dilution is measuring, is only equal to the percentage or proportionate error in the numerator and denominator. If the "1" unit were one drop and this was only accurate to within half a drop, then this is a 50% error and is huge, but if the "1" unit were 1 ml and were measured in a calibrated pipette, then the error could be as low as 1%. The "20,000" large volume can be fairly easily measured to within 1%, again assuming one has an accurate large volume measuring tool (for liters or quarts, for example).

I'm not sure how fcfrey is doing the measurements, but you bring up a good point about accuracy. The easiest way to determine the rough accuracy of a measurement is to try and repeat the measurement and see if you get the same result, especially if you go on the low/high side for the small/large volume measurement and then repeat going on the high/low side.

Richard

Richard/KurtV

When I diluted as in my last post, I dumped 1each – 182oz bottle of Clorox Ultra into a 6 gallon bucket. I then refilled the same bottle 3 times with pool water and combined these with the 7.2% bleach from the first step. To clarify --- that is 182 oz bleach and 546 oz water. This is a 1 to 3 solution ---- 4 parts total.

As for the dilution method for testing bleach I use a 1000 ml volumetric flask and a medical syringe used to perform the standard tuberculin “Tine” test. The syringe has a total capacity of 1 ml but is graduated in .01ml graduation intervals with major graduations at .1ml. Edit: The complete dilution method is only accurate to .1ml @20 deg C due to the accuracy of the volumetric flask ----- somehow I think that is "close enough".

Testing is done using the FAS-DPD method, using a 25ml sample size, again yielding accuracy within .2 ppm in a 10000 to 1 dilution.
If there is something wrong with the method please let me know. I have found the results to be repeatable with a 95% confidence level (in scientific terms [95 out of 100 tests]).

I am pretty anal with my testing methods.

Richard/FC,
Fair enough, I stand corrected.