Clownfish can host any number of corals, anemones, and things. I have heard of clownfish hosting power heads before. The best bet is to keep tank stable as far as rock work and introducing new inhabitants. My wrasse can bother my clowns when they are getting close to one another. Also they need a smooth surface for eggs to stick, having the right environment helps "set the mood". Also you should think of all clowns to be males, unless they are the dominant fish, then thats your female. It takes alone time for this sex change process to take place even if your fish are "sexually mature". When you place two random "males" in a tank it takes a while just to establish dominance, which is what cause hormonal changes in the fish. Helps if you choose a more sexually dimorphic pair, such as a larger male and smaller one, may help process along.