With fancy goldfish, just keep the diet simple and varied. They are typically slow eaters.. that is... they sometimes have a hard time collecting food from the surface but will always act hungry.
Golides are mostly veggie-eaters, so cucumbers, lettuce (parbroiled: dipped in boiling water for a couple seconds to sanitize it), zuchinni are good.
A little protein (fish meal) in fake food is good to. Nutrifin Staple flake food is cheap and does a good job.
I also use floating pellets, but more for my Koi and Comets, who can gobble them up quickly.
The trick is to keep the feedings small, regular and at the same time each day if possible so you don't end-up overfeeding goldies.