a 5 gal realy limits you in every way like ratio of hiding places and swimming area. the rules can be broke in most all cases by the environment around them. keep in mind this is from MY EXPERIENCE ONLY i have a 55 gal with 21 fish ranging in size from 8" to 1" and its a verry agressive fish tank. cichlids, bichirs, clown knife and so on but they ALL have at leaste 2 places to hide at any given time (for the big guys) many more for the small and vulnerable. but with this said a 5 gal just doesnt provide enouph room sorry, a 10gal is ok but i would go with 15-30. they are cheap take low maint and you just can do much more, good luck.