ok, i've got a nice new 5-gallon tank set up at school now, recently stocked with a young (1-inch) oranda goldfish. three days after i got him, he developed a tiny blackish spot on the tip of his dorsal fin. that hasn't gotten any bigger, but now he's got similar dark streaks at the ends of his tail fins, running right along the ridges. what on earth is this? the marks appear to be grayish-black, smooth, and small, and like i said, run right alongside the ridges on the tail. i've been doing regular water changes (10% or less about every other day, it was kinda cloudy) so i don't think it would be a high ammonia level... bacterial? fungal? whatever it is they're growing fast now. the fish doesn't seem affected but i'd really like to get rid of whatever it is!!!