Hi, and

!
Algae is a natural food source for goldfish, and I would leave a certain amount of it in the tank. I usualyl only clean the front and sides of the tank with an algae scraper or a rough aquarium sponge, and the rest I leave alone. The algae harbors good nitrifying bacteria, in addition to the filter, and I like the green carpet on the bottom and back of the tank.
I would avoid putting any kind of chemicals in the tank, even when they promise to take care of the algae. Most of them only take care of the algae that is free floating in your tank, thats when your water is green.
As for algae eating fish, most of them do more harm than good. They will eat off the slime coat of the goldfish, and leave them prone to parasite attacks....
I hope that helps a bit...