I wondered if 6% bleach equated to 6%=0.06=60,000 PPM of FC in straight bleach. Pool Calculator and a little math seemed to confirm this, so I decided to test to see if my bleach had lost some potency. (I bought 10 cases of 3x182 oz from Sam's Club over a month ago and the cases were sitting in the sun for a few days before I realized the stupidity of that.) I didn't suspect the bleach might be bad until today. Most of the time when I add bleach I don't bother re-checking FC level after adding, but just wait until it's probably time to add more based on typical FC loss and theoretical FC gain from the addition of bleach. I did a pre- and post-bleach addition FC check tonight (took average of 3 samples each time since I was testing what should have been an increase of 2.2 ppm according to Pool Calc, and I know from experience each test precision is only about +/- 0.5 PPM. Increase only came out to be 1.7 (Remember the precision is because I was averaging.) Anyway, there are too many variables there to conclude anything, so I decided to actually test the bleach. Here's what I did:
Combined 1 ml of 6% bleach with 6 liters of chlorine free water, which should be 10 PPM FC according to Pool Calculator's confirmation of the first sentence in the previous paragraph. Since starting to write this post, I have confirmed that my test worked, since I got 11 PPM (10% error is okay with me in this case!). But I still have the question which led me to create this post. After creating the theoretical FC = 10 solution (and stirring), I tried measuring by DPD titration, and the water "blinked" pink and went back to clear when adding the titrating powder. So I decided to give the K-1000 Cl tester a try. 5 drops of the reagent made the water orange (very close to the pH=7.5 color on the pH test). I assumed this meant a very high FC concentration. About an hour later (after beginning this post which was originally intended to ask if my test should theoretically work, and if so, what I might be doing wrong, but it turns out all I did wrong was not waiting long enough to test it. Apparently the chemical reaction H2O + NaClO --> ... (Richard could finish this if I've even got it started correctly) had not finished. So whatever form of Cl the tests read (HClO?--I think I remember that being the "working" form of Cl from previous reading in the Deep End) hadn't formed yet.
I'm sure others have conducted a similar bleach test to the one described above, but it was really neat to see the theory work out experimentally! (By the way, in case you're wondering, the water in the mixture was filtered, basically chlorine-free. Aquasana rocks!)
Now that all is said and done, I might be sorry I asked, but why did the K-1000 test turn orange and why did the DPD test "blink" pink?