Got a 10" CK. He's awesome in the tank. Been droppin some lancefish in, he bites 'em then spits em out. Krill, massivore pellets..?? I dunno, I know he wont eat. I am sure he will when he gets hungry. But, what do you guys feed your knives???
Mine's go crazy for bloodworms. I use Hikari frozen bloodworms. I tried Frozen krill, but he doesn't eat that. He'll pick on the massivor delight, but the bloodworms by far gets the best reaction from him. My ck now is about 10". I also use a heater for his tank with the temp @ about 87-90 degrees. He's gotten alot more active and hungry since then.
Bloodworms usually work to start off on...then adding pellets and whatever. They do seem to have an easier time, at least in the beginning, finding food that is sitting on the bottom of the tank rather than hitting it while it's floating in the water. Also might want to feed with the lights off, maybe some ambient lighting in the room so you can check that he is indeed eating. How long have you had him? Tank mates?