So for about a month now I've had problems with one of my six green chromis. It sits in a hole in one of my decorations and it rarely comes out, even for feeding. We have to get a clump next to it for it to come out. When it comes out, it's very pale, almost white. It's medium sized, not very big but not very small. It's fins look fine and I haven't seen it getting picked on. It doesn't look sick either besides the coloration. What do you think it is? Should I move him to another tank to see if he gets better?