Depending on the timing and the source, there can be a couple of different methods to adding Live Rock to an aquarium. Most hobbyists purchase the majority of their Live Rock when they are first setting up their mini-reef aquarium. Any time you receive “raw” Live Rock, it is best to dip it in a bucket of freshly made saltwater and then take a soft brush to knock off any loose debris. Once the rock is cleaned, you should place it in a curing tank with saltwater, or into the new aquarium filled with saltwater. In either case, you want to have lots of water movement and an efficient skimmer will also help control the wastes put off by the curing Live Rock. If you are using a smaller container to cure the Live Rock, you may want to do a large (60-100%) water change after 2 or 3 days. If you are curing the Live Rock in the main aquarium, you may want to add some AmQuel or Ammo Lock II to help protect the live bacteria from the high ammonia levels. Monitor the ammonia, then nitrite levels, and, once they are both back down to 0.0PPM, the Live Rock is considered cured and safe for the mini-reef. When placing the Live Rock in the aquarium, be sure that the bottom rocks are firmly on the bottom and there is no way for the fish to cause a cave in by digging out the sand under the rock. If any of the rocks tip over too easily, you can support them by using one of the underwater epoxy stixs to glue the rocks together. If you are attempting a large arch, you can literally drill out small holes and use acrylic rods like dowel rods to tinker-toy the rocks together and then use epoxy to help anchor the rocks in position. You can also use zip-ties; they will soon be covered with coralline algae and fade into the rock.
Placing freshly cured Live Rock is actually a bit easier than placing cured rock that has been in a system or aquarium for any amount of time. This rock would now have “light areas” where new growth may have occurred and when you reposition it, areas that were in light may now be placed into the dark. This can lead to more die-off and a possible ammonia surge, so care should be taken to monitor the water quality and to be ready to make a partial water change if needed.
One common misconception about Live Rock is just what do we mean by Live Rock. For the purpose of filtration, we consider rock that is “Live” to have massive colonies of the nitrifying and denitrifying bacteria. Any other growth on the Live Rock (sponges, tube worms, coralline algae, etc) is a bonus. Most Live Rock, after curing, will look like a gray rock with not much growing “on” it. It is best to take a picture and then 6 months later look at the tank, and you will not think it is the same rock. You can also use pieces of Live Rock to seed dry, base rock and eventually this rock will also become a “Live Rock” biological filtration system.
Larger pieces of Live Rock will have cores that are colonized with the denitrifying bacteria that thrive under anoxic conditions. While this will help with controlling nitrate levels, most mini-reef aquariums do not have enough Live Rock to totally eliminate the nitrates. Additional rock placed in a refugium sump or a dedicated denitrifying reactor would be needed to eliminate the nitrate.