Im thinking of setting up a marine tank in my 125ltr. I've got quite a bit of ocean rock in it from a cichlid set up and I was wondering if I bought one small bit of live rock and put it amongst my ocean rock will it spread so I end up with all or alot more live rock? I've also just bought a Boyu EF-20 external Filter which is for a tank twice the size of mine. Would this be ok for a set up? Will probably also get a HOB protein skimmer. Have I read right that with this tank(33 us gal) I won't need the external filter eventually?? As the live rock will do the job? I'm not after a huge amount of fish. A pair of common clowns and maybe a cardinal and some thing else small and interesting. All feed back welcomed. Thanks in advance, Ben