About a month ago my capranis developed this white spot on his dorsel. At first I thought maybe it was just damaged from running in to something, since it showed up more or less overnight. It's been a month and it still there. It hasn't changed in size or color. None of the other fish have it. The pic's are the best I could get of it. Any ideas what it is or how to get rid of it? It's abiut 2-3mm.