Sounds like maybe whatever it is is not water soluble, if you washed it. I have removed fungus from the emulsion of film, plus anything on the base side with a 50/50 mix of isopropyl alcohol and distilled water. I was able to get actual 99.xx% alcohol by requesting it at a Target pharmacy, a gallon was about $30 (lifetime supply). I soaked the negs (4x5) in a small tray for 5 minutes or so, then swabbed very gently with cotton balls, in the tray, then a quick wash, then P-flo, then hang. Nice and clean.