I have a 75 gallon tank with 20 gallon sump and all water parameters are zero except for nitrates which is at 10 ppm. I have a long nose butterfly fish and I just noticed there is one white speck on its fin. The fish is acting normal, eating properly and not rubbing against anything. I am not sure if it is ick because ick normally as white specks all over the fish's body. What could this white speck be?