Re: Can tank size limit fish size? (Or why are my friends fish so small?)

10G is typically enough for fancies, if you are willing to put the
time in to do regular maintenance (25% water change once a week which
includes substrate vacuuming).

Also never feed your goldfish just because they look hungry. 
Goldfish are scavengers. once or twice a day is enough. Goldfish always
look(pretend) hungry