Ah ...now the question is ... are you looking to keep goldfish? If so ... for 5 goldfish your looking at a 60 gallon at least. "common" goldfish can grow up to a foot I believe. Fancy goldfish can also get several inches large ... that and the large bio-loads is why you need large tanks with really good filtration.
If your willing to switch to tropical fish ... your looking at a 20 gal
al least to have 5-7 fish ... molly's or platty's. IMO
a 10 gal
is really only suitable for a male betta, shrimp, snails and or to serve as a hospital QT tank.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.