geez I seem to have a lot of trouble with my fish (suicide, disease, fighting)... anyways, I have 5 white cloud minnows (20 galllon tank), three of which were used to prepare my new 30 gallon tank... they've been reunited with one another, but one of the minnows (which I don't believe to be one of the tank transferees) has become extremely dark in color... all my other fish are healthy, but I wonder about this one... any ideas? thanks