http://www.reefsanctuary.com/forums/...ck-anyway.html
quote: some aquarists claim that live rock should be replaced every 5 to 10 years. The lifeforms inside the rock will die off of their own accord, and the help the live rock gave at removing nitrates will diminish as the rock ages. Some claim that once coralline algae covers over the crevices and these worm holes, that the rock will loose its ability to handle nitrates, too.
Good read... anyways