The powder is a light grey, I dont think it is bleaching it out, I showed around 2 ppm with the oto test, then I took water sample from my pool and wanted to see if my dpd powder was working so i added str8 bleach to the sample just to get a reading, so it might have bleached out the powder that time but before I did that my oto showed 2 ppm and powder showed none and then when i added str8 bleach my dpd still showewd 0 but oto turned burnt orange , If that makes since.