Feed them anywhere from pellets, worms, bloodworms, krill, shrimp etc....as long as they accept the food. A varied diet is always the way to go. Smallest I believe are to be Scobina and Hystrix. But both aren't very cheap either. I believe both these species can live in 30" wide tank. And your 150 will only last until it's lenght is longer than your 18" width on your 150. (assuming your's is the average 150).