Live rock is rock from the ocean that has been introduced into a saltwater aquarium. Along with live sand, it confers to the closed marine system multiple benefits desired by the saltwater aquarium hobbyist. The name sometimes leads to misunderstandings, as the "live rock" itself is not actually alive, but rather is simply made from the aragonite skeletons of long dead corals, or other calcareous organisms, which in the ocean form the majority of coral reefs. When taken from the ocean it is usually encrusted with coralline algae and inhabited by a multitude of marine organisms. The many forms of micro and macroscopic marine life that live on and inside of the rock, which acts as an ideal habitat, give it the name "live rock". Origin Live rock is harvested for use in the aquarium from reefs, either from natural or human breakage. It may also be "seeded" from small coralline rocks by an aquaculturalist in warm ocean water, to be harvested later. Live rock can also be seeded by adding base rock to an active reef aquarium that already has live rock. Live rock harbors a wide variety of corals, algae, sponges, and other invertebrates, when they are collected. Corals added to the aquarium later will often become attached to the rock. Purpose Live rock is highly valued in the aquarium trade. It introduces a diverse array of bacteria, algae, and invertebrates to the closed marine environment and functions as a superior biological filter that hosts aerobic and anaerobic nitrifying bacteria required for the nitrogen cycle that processes waste. Live rock becomes the main biological nitrification base or biological filter of a saltwater aquarium. Harmful elements dissolved in the water of the aquarium, including ammonia, phosphates, and nitrates, are processed with the help of the organisms that are introduced from the live rock into the aquarium's ecosystem. Excess ammonia, nitrate, and phosphates are eliminated with the help of the algae and corals growing on the live rock's surface, while other bacteria supplement the process and restore balance in the water chemistry. Additionally, live rocks have a stabilizing effect on the water chemistry, in particular on helping to maintain constant pH by release of calcium carbonate. Lastly, live rock, especially when encrusted with multiple species of coralline algae (producing differing colors), becomes a major decorative element of the aquarium and provides shelter for the inhabitants. It is often used to