I have had two percs that are about 3/4 inch for three weeks. I noticed about a week ago that one has a "cotton ball" looking growth on one gill. Today I noticed a smaller but similar growth on the back below the tail of the other. The tank has a six line wrasse and lr with mushrooms. Clean up crew, pepermint shrimp and a cleaner shrimp. Water looks good, percs act fine, eating ect. These were "tank raised". I do 15% wc once a week. I was thinking it was damge turning the transfer, but now I do not know.