I noticed a tiny blemish on the dorsal fin of my favorite discus - I just bought him, he probably had it from the store. The next day it was a wee bit bigger. I am assuming it will be worse yet today when I arrive home from work. I tried scoping out the disease database on this site but did not see "fin or tail rot" and I do not know the scientific name ... can anyone help me out? What's it called, what do I do to treat it? etc ...