[Sk8r]

Not true.
You have to get 'reef-safe' fish. This, understand, doesn't guarantee they won't eat each other, but there are hundreds of species you can have in a stony coral tank.
Look on liveaquaria.com in marine fish. If it says reef-safe, it will probably be fine.

Fish that ARE safe: blennies, gobies, [dragonets: mature tank only]; dartfish; damsels [chromis is the safe one: the others are nippy toward other fish]; kole or tomini tang [other tangs grow too large for your tank: these two max out around 9 inches, as I recall, but check.]

Fish that are not reefsafe: angels, butterflies, puffers in general, and a few others.

Fish not safe with other fish: eels, triggers, sharks, cephalopods: the carnivores.

Reef fish measure adult size in feet, in some instances: before you get a fish, check that out on that site. THey never stop growing.

Fish with a max size of about 4-5 inches will be most comfortable in your tank.

Beyond that, ask about habits and compatibility.