You mean like those nano style tanks? Those are okay for beginners but only get small gobies(stay away from mandarins or scooters) or clown fish, gentle shrimp like skunk cleaners or sexy shrimp or small hermits and easy corals like xenia and zoanthids.
my mandarin did well in my 24 gallon nano. but im some sort of expert

honestly i got lucky, some of them dont last because they are picky eaters, but i got some sort of... well, something, in a squirt bottle that had little dead orange things that cost 30 bucks a bottle. but he or she really liked it.
