I have started treating for fungus using Fishkeeper from my local aquarium store. If that does not work il go to the chemical stuff I guess. I think my other angel fish may have died in the tank and my daughter didn't see it so it contaminated the water. I've done a water change and cleaned the filters. All the other fish appear ok with no outward signs of stress. I have some tetras and a couple algae eaters as well as a rainbow shark. Please let me know if I should be doing something more aggressive or if I need to separate him. In the three years of having my tanks I have not had to deal with this. Thank you!