My royal love potato. He eats 4 halves a week. He also goes for sinking catfish pellets, earthworm sticks, kiwi halves, bloodworms, frozen peas, and fish fillets. Make sure you keep some driftwood in the tank for your royal to chew on. They get nutrients from the bacteria that lives on the wood's surface. My royal grinds down over 50lbs of wood a year.
The pic is a little over a year old and taken when he was a mere 18".