goldies need veggies. mine go crazy for zucchini. steam it up like you would for yourself, cut to size and plop it in. mine eat the lot, skin, seeds and flesh, but i know some people strip the seeds and peel them first...
i also swap between frozen blood worms, frozen brine shrimp and live brine shrimp (coz its fun to watch them chase them all over the tank. i have a 6 footer

)
but xDCxSMOKE is right, you have to have a good quality flake food.
how big are the fish and what type of goldfish do you have?