I recently purchased 6 new fish. 2 emerald green Cory catfish, 2 peppered Cory cats, and 2 albino bristle-nose plecos. I put all 6 of them in my 10 gallon quarantine tank to first see if they show any signs of disease or infections, and only one has showed any symptoms. One of the peppered Cory’s has this weird growth on the top that keeps getting larger. I started treatment 3 or 4 days ago with General cure and e.m. Erythromycin. Can someone help me identify this infection and/or what else I should do. All of the other fish look completely healthy. They all eat and swim very much.