I *really* hate this idea of no filtration but liverock and turnover, its a personal thing and i dont care how many people prove that the water quality is just great with no real filtration...
To be honest it limits it if you want to mess around with stuff like rowaphos or a refugium etc or sponges, if you have nothing to take the crud out the water, in the long run you just get one of those tanks full of so much muck. Urgh would drive me nuts.
I had FOWLR tanks running on the biggest Classic Eheim External and thats it, all it had was 5 round sponges and i cleaned it every month.. ish.. maybe 2-3 months as depended on what i was feeding, it didnt do too much but did clear the water.
Internal filters are no good on marine, the metal parts generally rust and clog up with all the crustaceans determined to live in it. Honestly.
You can pic up decent external for pittence on fleabay!
I ran tank without a skimmer, but being bigger fish, even without corals etc, id NEVER run one without a skimmer again, filthy ruddy fish! I had 2 x Yellow Tangs, 1 x Juvenile Passer Angel and 1 x Juvenile Volitans (tangs were maybe 3" nose to tail, passer maybe 2.5-3" and the Volitans was 1" to start with and ended up 6" before he kindly wiped out tank for me). Tank was 260L sorry. With powerhead and eheim, think it was 2217? biggest classic either way..
Skimmers are important either way i think unless you are brave or determined to make things harder than is needed
FOWLR generally means fish with high protein diet = lots of waste.. = protein skimmer is sensible!