I have a goldfish - it's in an aquarium with two other goldfish, who I think are common goldfish. I haven't been able to identify the exact sub-species of the one in question. It's mostly a dark, dullish shade of orange - with a black stripe up its back and black on the end of its tail. Recently it's pretty much stopped eating, and has developed a thin white coating. It also goes up to the top, between the water and top, frequently, which I heard could be a symptom? Is it sick?