My black neon tetra that I've had in my 46g planted aquarium for 2 years is sick. He lost almost all of his color and has been darting aimlessly when I get close to him. He also has a reddish color on his top that looks like a small amount of internal bleeding. The weird part is that he has been this way for over a week with no signs of getting better or worse. He's in a hospital tank. None of my other fish are sick