Simple Bleach Strength Test w/ 5 Reagent Bottle Drops & 2 L Bottle

karcherd

Bronze Supporter
Mar 28, 2017
12
Fayetteville
Atwood's was out of 10% chlorine so I had to pick up a few cases of their ordinary bleach (concentration unknown), and I need to know the concentration in order to use Pool Math. I found some great info in older threads for determining bleach strength by creating a 1:10,000 dilution and then performing a standard FC test. However, the dilution part seemed a bit tricky and a source of potential error, so I thought the following might work with some items that are at hand:

1) Carefully pour a little bleach to be tested into a clean, empty Taylor reagent bottle.
2) Fill a 2 liter bottle halfway with chlorine-free water.
3) Use the reagent bottle to add 5 drops of the bleach to be tested into the 2 liter bottle.
4) Completely fill the 2 L bottle, cap it, and shake a bit to mix thoroughly.
5) Test the solution in 2 L the bottle using standard methods.
6) The resulting Cl concentration from the FC test should equal the sodium hypochlorite concentration (%) of the bleach.

I'm relying on the following info for this to work. Previous posts have indicated that Taylor reagent bottles are designed so that 24 drops equal one mL. So, 5 drops would equal 5 * (1/24) => 0.208 mL, which is roughly 1/10,000 of a 2 L bottle. I write "roughly" because it is actually a 1:9,615 dilution, so, we need to multiple by 1.04 to correct for this (1.04 = 10000 / 9615). However, even with out the correction the estimate should be accurate enough for Pool Math purposes. Math and chem geeks, please check my methods and let me know if I've made errors or bad assumptions.
 

tillmac62

Well-known member
Sep 30, 2019
73
Gaffney, SC, United States
Take 0.1ml of your "bleach" and dilute to 1 liter. Test this sample as you would your pool/spa sample (10 ml using the FAS-DPD) method. The result, in this case, is pph (%) rather than ppm. For example, a 6% bleach concentration will yield 6 as the test result.

Dilute with distilled water.
 
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karcherd

Bronze Supporter
Mar 28, 2017
12
Fayetteville
Thanks for the reply tillmac62. Your method is sound, but my main issue is how to precisely measure 0.1 ml of "bleach" as I don't have a ready supply of 100 micro-syringes. However, I do have plenty of used, rinsed reagent bottles that can dose a precise 5 drops... and plenty of 2 L bottles (they originally contained tonic water... see profile pic :).) I just now tested my 5 drop method above with Atwood's bleach and got 3.0 ppm Cl with the FAS-DPD method, so I assume it is 3% bleach, which for $1.19 isn't a terrible deal, but not near as good as their 10% liquid chlorine for $2 a gallon.

The 5 drops and 2 L bottle method was very simple to do and required no precise measuring (with the use of a Samplesizer). Also, I used tap water, because I do not keep distilled water on hand. I've assumed this is okay because there is no measurable FC in my tap water according to the FAS-DPD test. Please let me know otherwise!

I've benefited A TON from this site, saving a lot of time and $$$ while maintaining high quality pool water, so it would be great if this 5 drops / 2 L bottle method might help a few others out there to quickly verify bleach strength. And now, I'm off to work on emptying another 2 L tonic bottle for future bleach testing. Cheers!
 
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karcherd

Bronze Supporter
Mar 28, 2017
12
Fayetteville
Correction, I think the correction factor is to divide by 1.04 (or multiply by .9615)... however, the estimate seems to be close enough for practical purposes without this step.