everything i have read points towards two facts:
1:
fish need a minimum volume of water
2:
fish need that volume of water to be in a shape that suits their species
example:
the general rule of thumb for marine tanks is "for every inch of fish you need 5 gallons of water"
with that said, an 8 inch yellow tang will not fit in a 40 gallon aquarium because tangs like to swim fast and for long periods so they need a tank with large dimensions, i think it comes out to 80 gallon minimum.
on the other hand a 3 inch goby can live in a 10 gallon tank because he likes to hang out in one spot most of the time.
lol all in all i cant advise on the species of clown you have, because i lack the experience. but i hope the above information helps. I have, however, read from reputable sources that Ocelaris clowns are happy in a ten gallon tank if there is only one fish in the tank. But i believe the maroon clown gets twice the size of the Ocelaris. And clowns are active swimmers. They pick a place in the tank to call home and "host" an ornament or pump or coral, and explore in large circles around their home.
hope that helps.