Eating is definitely not a problem. He is at the top of the tank with the others every feeding time and he gets his fair share. If it is stress it must be one of the others stressing him out. My lfs had the group for about two months and he was black the whole time. They actually threw him in for free since they thought he might be sick or a hybrid. But as soon as they bagged him he instantly changed to normal colors. And they were all in one bag. As soon as I put him in the 120 he went right back to black. He acts normal and eats fine just shows alot of black. When he was showing normal color I noticed one thing, all the others have alot of yellow and he is more of the silver. I don't know if that makes a difference.