None. The only fish that can realistically live with goldfish are other goldfish due to differing housing, temp, & feeding requirements. Algae eaters are known to suck the slimecoat off of goldfish which will create a plethra of health issues for the goldfish as well. The only creature you can safely house with goldfish are some very large snails- smaller ones will be eaten. Regular water changes & tank cleaning will help keep algae issues under control.