Live Rock in Marine Aquariums
Live rock explained: how it provides biological filtration, the curing process, the difference between dry and live rock, and its role in aquascaping.
What live rock is
Live rock is rock used in saltwater aquariums that is colonised by marine organisms. Despite the name, the rock itself is not alive; it is made from the aragonite skeletons of long-dead corals. During time in the ocean and transport it becomes populated with bacteria, algae and small invertebrates, and it is these colonising organisms rather than the rock itself that make it valuable in an aquarium.
Biological filtration
Live rock acts as the main biological filter in many marine tanks. It hosts both aerobic and anaerobic nitrifying bacteria needed for the nitrogen cycle, helping process ammonia, nitrite and nitrate. The calcium carbonate it is made of also helps stabilise pH.
Seeding the tank
When added to a new tank, live rock introduces a diverse range of bacteria, algae and invertebrates into the closed system. This establishes the microbial communities that an aquarium needs to stay biologically balanced.
Curing live rock
Harvesting and transport kill some of the organisms on the rock, which can cause an ammonia spike. Curing involves keeping the rock in water for up to several weeks so that dead material decomposes before the rock is placed in a stocked display tank.
Dry rock vs live rock
Dry rock, also called base rock, is aragonite rock with no organisms growing on or in it. It is cheaper and can be artificial, such as aragocrete, a concrete mixture. Over time dry rock becomes colonised by bacteria in the tank, gradually taking on the filtering role of live rock.
Aquascaping and shelter
Besides filtration, live rock is used to build the aquascape. It provides structure and shelter for fish and invertebrates, allowing the construction of caves, ledges and other features within the tank. Because the rock also releases calcium carbonate, it contributes to buffering and helps keep the system's pH stable over time.