I have a 10' royal and a 8" clown knife in my tank. Both of them are very active and I've trained both of them to eat from my hand. It took me about a month to train them but it wasn't very hard. Try starving him for about 3-4 days, then put your arm in the tank and hold a live feeder by the tail in front of him about 5-8 inches away from his mouth.It took my fish ten minutes before he ate from my hand the first time, it'll probably take a few tries of this before he'll get used to your hand in the water but when he gets comfortable eating feeders from your hand, then swith to other foods like food sticks, krill, crickets.... after a month, I was able to get my clown knife to eat from the surface of the water from my hand, the royal knife however is a little lazy and prefers to be fed from the bottom of the tank. The best food I've found to help all my fish grow was crickets. Both of my knife fish are a year old and I got them when they were about 3 inches long.