Filters aren't meant to clean algae, and goldfish aren't meant to live in 10 gallon tanks. A fancy goldfish needs 20 gallons, minimum, and a common or comet needs 55 gallons BARE minimum, and even then that's rather small. You need to understand that goldfish are very large, very messy fish and need huge tanks with LOTS of filtration.
http://www.peteducation.com/article.cfm?c=16+1922&aid=2650