I currently house my pacman Jimmy in a ten gallon tank. Initially I got it because I wanted to have a nice enclosure with aesthetic touches to it, but I feel it's just too big for him (he's about four months old). Is a 5.5 gallon too small for him as he starts to reach adulthood?

It just seems like the tank is too big for him to hunt in. I have to tong feed him. I've trained him on tongs but would like the flexibility of dropping live food in there and letting nature take its course.