Black Ghost Knife...who has em?

Ive had these before. We got this one about a year ago. He was only a couple inches long when we got him, now he's probably about six inches. He eats carnivorous sinking pellets and shrimp pellets. we used to also have a ropefish and tetras, but the tetras went back to the fish store, and the rope fish went carpet surfing and was out of the tank too long. So now its just the knife, and I'm not sure how much to feed him! I guess I'll figure it out. He looks round enough.

Who else has this fish?