High amounts of DPD Powder needed!! To high or no Clorine?

[CarlD]

OK, I'm confused. DPD is usually either a drop or a tablet. The OP said DPD powder. That sounds like FAS-DPD powder. If so, it won't bleach out at 10ppm, but regular DPD will. Sounds like apples and oranges to me.

Carl

[chem geek]

DPD powder used in the FAS-DPD test can indeed bleach out at levels > 25 ppm. One gets a "flash of pink" and then it goes clear. You then add more powder until you get a color. It sounds like the Free Chlorine (FC) level is very, very high -- perhaps above 50 ppm given that it took 3 scoops before a color was seen. To test such a high FC sample, one can dilute with distilled water so that one can save on reagent and one can also use a smaller sample size (10 ml is 0.5 ppm per drop; 5 ml is 1 ppm per drop).