Asker's rating. Report Abuse. Well a small tank, 10-20 gallons, is probably only a good size for 1 goldfish and moving a goldfish from a pond to a small tank is probably not a good idea. I would just go and get a good quality oranda or fantail goldfish cuz they are only like a dollar. hope this helps ^_^.zaviort · 7 years ago. Thumbs up.sker's rating. Report Abuse. Well a small tank, 10-20 gallons, is probably only a good size for 1 goldfish and moving a goldfish from a pond to a small tank is probably not a good idea. I would just go and get a good quality oranda or fantail goldfish cuz they are only like a dollar. hope this helps ^_^.