Instructions
Rinse the old live rock in a separate, saltwater bath, shaking off the rock to dislodge and remove any dead or decaying organisms lodged inside.
Layer the old, "dead" live rock on the very bottom of your tank. Don't add too much, as too much live rock in one system could quickly die off, and you will be left with an abundance of dead rock on your hands. Overall, you want about 1 to 2 lbs. of live rock per gallon, depending on your tank setup. 1 lb. per gallon should be used in tanks with saltwater fish, and 2 lbs. per gallon in reef tank systems.
Install a batch of new live rock; obtain it from your local pet store or aquarium shop. Just as you did with the old live rock, bathe the new live rock in a saltwater bath and shake loose any dead or decaying material.
Layer the new live rock atop the old live rock. Over time, the life in the new live rock will drift and migrate into the old rock, reseeding it.
Inspect the live rock for signs of decay, such as water-clouding and black growth on the live rock. Remove decaying live rock from the tank immediately to avoid contaminating the tank.
How to Reseed Live Rock
Live rock is naturally broken-off coral sold in aquarium shops to help maintain saltwater aquariums. The organisms living inside the live rock, such as crustaceans, algae, crabs, marine worms and bacteria, help establish a natural biological filter for saltwater tanks. If you have old live rock, and would like to reseed it for use in your tank, reseeding is relatively easy.