Clarkii's are more aggressive than ocellaris'. Give them time and they might host (it took mine a long time before they hosted). I made the mistake of adding a Clarkii (not knowing they don't get along) because I had an extra BTA. The clarkii evicted the ocellaris' from all of the BTA's. Fortunately for the ocellaris', they clarkii was found carpet (well, hard wood) surfing one afternoon.