For the past two weeks he's gone off into one of the corners in the tank and just lays down on its side. I figured it was sick but when a fish goes near it he'll get up and swim around normally for a good while. And when I put fish in the tank it goes crazy. Its odd because it looks like it may be sick but other than lying down or just sitting at the bottom its active. Its a 50 gallon tank and not overcrowded so I ruled out stress.