|Yes, this is true. By adding small amounts of new uncured live rock to your established reef aquarium, you will add new, beneficial organisms. Plus, these organisms will likely survive the transition, since they will not be subjected to the ammonia spike which commonly occurs when curing large amounts of rock. At the recent International Marine Aquarium Conference (IMAC), Dr. Ron Shimek emphasized the importance of diversity among the organisms in your live sand bed. This diverse population helps ensure adequate processing of detritus and leftover food which, in turn, helps lower nitrate levels in your aquarium.
When exchanging live rock in your aquarium, do not exchange more than 20% of the total amount of rock, then be sure to give the aquarium a few months to stabilize. The original live rock and your biological filtration will process the nutrients added with the new rock. Be sure to monitor pH, ammonia, and nitrite levels during this time. If fluctuations occur, perform water changes and add appropriate chemical media to compensate. It is best to place this rock low in the aquarium on the sand bed to allow the organisms easy access to the live sand.