Ryukin Goldfish TIps? Please help!?

I just got a ryukin goldfish and right now he is in a 30 gallon tank with my Black Moor. What should I feed him? Are there any diseases that I should know about? How big and how old can a Ryukin get? Are there any treats I can feed him other than the flakes? How can I keep him and my black moor happy? Serious answers only, please. Thanks! :3