[aninjaatemyshoe]

It would be a great idea to swap rock, assuming we're talking about rock that has been properly handled, quarranteened and matured. Garf does something similar with their "reef-grunge."

I think the real problem is that, no matter what you do, the biodiversity will decline in your tank as time goes. As a closed system, you're dealing with less than ideal conditions. Certain species will outcompete others and take over and gradually you will have fewer and fewer species. The problem is worsened when you have things like planktivorous fish and predatory corals that will quickly do away with things like copepods. The only real solution to this is to refresh your tank with new live rock every now and then.