Throw some food in about 30 mins after lights out. Mine are 10" after 5 months. I'd say your lucky, but something is stunting their growth. In case you didn't know they can get to over 3ft in aquarium. 4ft in the wild. Hope you have a pond or something planned. They are fine outside too. I'd say more than likely it's diet more than anything. You need to feed him enough so that he's not just eating leftovers. He should look pleasantly plump after a feeding. Try cutting up some market shrimp small enough for him to eat. That's what I give mine, and they grow like weeds. lol. Good luck.