I have a question about the FAS-DPD combined chlorine (CC) test, in the Taylor kit. I'm using the sample size where each drop represents 0.2 ppm of chlorine. I did the FC test first, and the pink color completely disappeared after 18 drops, indicating the FC is 3.6 ppm.
Then I added 5 drops of reagent R-0003, to test for CC. The sample just barely turned pink. Viewing it from the side it appeared clear, but when I looked straight down into the tube it was just barely detectable pink. The instructions do not tell you to look straight down into the tube when doing the CC test, but that's the only way I could detect the very faint pink tinge.
When I added 1 drop of R-0871 and swirled, the pink completely disappeared. So I figured that means I have some CC but no more than 0.2 ppm. However after several minutes, I noticed the very faint pink color had returned. So I added one more drop of R-0871 and the pink completely disappeared again. So I figured that maybe I have 0.4 ppm of CC. But after several more minutes, the faint pink color returned, and if I waited even longer it got more noticeable.
So I can't tell how much CC I really have. The test kit instructions do not say anything about waiting any period of time when doing the CC test. Should I just count the number of drops needed to initially get rid of the pink and ignore the fact that it returns after several minutes? As I said, after I add the 5 drops of R-0003, and swirl, the pink color is so faint it is only visible when looking straight down the tube.
As background, my CYA is about 45, pH=7.6, TA=100. The pool was refilled a couple months ago and everything else is in a good range. I'm only using bleach and I've been consuming about 3 ppm of FC daily, mainly due to sunlight (no swimmers for the last few days). I add enough to get FC up to about 6 to 7, and then it's down to 3 to 4 by evening. So I think I'm maintaining FC correctly, but it's the CC test that puzzles me. We did have a lot of swimmers 5 days ago so I figured i might have some CC from that, but I can't tell how much.