hello! I have 2 rainbow fish, each with different "problems". The first question is i have a very healthy one, has a nice dark black color but has a spot on the back of his body (near the tail). It's a white/gray spot. I was wondering what this is? it doesn't seem to be getting any bigger but I'm worried it may be a body fungus of some sort. if so, what would be best to treat it with? second question about the other rainbow fish. he seems to be a healthy fish as well but he's turned more of a grayish color than black. now, in the last week he has gained some of his black color back but is still not as black as the other one. I was just wondering if this is something i should be worried about. It is obvious that the darker one is the dominant one in the tank so could it be that the lighter one is stressed or maybe that this is just the way he is colored? thanks!