I solved all my photoflo problems recently. I always had the hardest time getting a dilution that seemed to do anything, and didn't leave (fairly benign) marks on my film occasionally. I'm not sure if it's because I use 18 megaohm ultrapure water or what, but the stuff foams too and little bubbles get caught in the sprocket holes. I think I finally have the optimum dilution nailed down. I don't have any problems and get perfectly clean negatives at 0% photoflo, by volume. My bottle should last a long time this way too.