in general it can and is done, but i have two tanks at work both 300 litres, a reef tank that has tones of rock corals inverts and fish-tang gobies chromis hawks clowns a great sump fuge n all, then ive got a invert tank same size next to each other, tones of coral inverts rock sump fuge all the same, lighting but with only a yellow tang, do all the same maintenance, first tank the reef tank nitrates stay around 20-30, second tank 0 nitrates ALL the time, the second tank just looks better in general, corals are brighter water is the best it could be, i also have a fish only tank the same. the esiest tank to look after and maintain perfect water is the second invert tank, the reef is the hardest and the fish only in the middle, so the less fish you have in a reef tank the esier it is to maintain water quility, but you do need one fish to feed the tank- its the esiest marine tank to do, the invert tank, its just so balanced with one fish, the corals and inverts love it without the stress of more fish.........ok im done LOL