How can I test bleach for myself to confirm the concentration of Sodium Hypochlorite?

dclynds

Well-known member
Apr 29, 2016
73
Houston, TX
In the absence of my standard go-to 6% bleach at aldi, I went to Pinch A Penny Pool Supply and got a 2.5 gallon jug of supposedly 10.5% Sodium Hypochlorite. I am skeptical of that 10.5% concentration. Yesterday, my FC was 4.0 pp. , so I added 40 oz yesterday which should have bumped FC up by 2 ppm. However, when I tested again today, the FC was 3.5 ppm. Very surprising! Besides monitoring effect of pool water over time, what is a quicker and more direct method to test a sample of bleach directly to determine its true Sodium Hypochlorite concentration?

Thanks,
Daniel
 
Yes. 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.
 

dclynds

Well-known member
Apr 29, 2016
73
Houston, TX
Yes. 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.
Take 0.1 mL and dilute to 1 liter? 0.1 mL seems like an awfully small volume so just double checking. Thanks for the help
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
26,604
Laughlin, NV

I messed up in my post above. It is 0.1 ml of 10% to 1 liter of water for 10 ppm.

You are better off adding to your pool and determining the approximate % that way.
 

griffths

LifeTime Supporter
May 2, 2011
159
Long Grove, IL
I just looked into this and you can purchase the reagents for about 70.00 and store in your own box. Still not sure if I am willing to bite, however I do purchase in bulk and usually end up with multiple cases in the basement over the winter that I am curious about.

Empirically, the bleach does seem to be equally as effective in the spring as the previous fall but it would be nice (in an OCD way) to know exactly how much it has degraded over the 6-7 months it has been sitting in the basement.
 

Oly

Gold Supporter
Jun 28, 2017
1,254
Fresno, CA
As mentioned above use pool math to estimate the result of your adding a known quantity of the chlorine liquid you have available. Test your pool water for FC before and after an hour of the application. Confirm the FC result and if different from your earlier estimate, alter the % bleach in pool math to find your answer. OCD relief with the test kit you already own.