All of the equipment on the Pacu's tank is located in the sump. Before that they figured that if it wasn't food it was a "chew toy". Airlines, overflow tubes, plastic plants etc.
They will eat algae wafers , peas. string beans, as well as wtat has been previously mentioned. Grapes should only be an occasional treat (sugar content) they shouldn't have very much, or very often.
I only have 15, all rescues & they will always tell me that they are hungry. They get fed once a day, feeding more often can lead to additional water problems.