They can be very reclusive. Mine, named Chester, was often out in front in the 75. Then I moved the tank and during the move I didn't see Chester at all. He actually got into one of the holes in the LR and was transferred from one of the tanks to the other, twice, without ever being seen. While he was in the temporary tank, I literally never saw him. Then when I got the 125 complete, I thought he was just gone. He popped out one day but still remains in the shadows. I'd say give him time and consider whether there are any other fish that might be intimidating him.