My German Red Peacock has a couple of areas on his tail that look like someone scribbled on him with a black sharpie. He is perfectly healthy otherwise. These marks have been on him for several weeks. I have had the fish about 6 months. Does anyone know what causes this and how to treat it. This is not Black Ich. The black areas are not raised. No other fish in my 150 Gal tank has this and my water quality is perfect. I do 50% water changes weekly. Any input is appreciated.