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Live Rock
The Foundation of Most Successful Marine Aquarium Systems

Let us talk live rock, shall we? Many marine aquarists add the requisite one to two pounds of live rock per gallon without truly appreciating the benefit it brings to the health and stability of a saltwater aquarium. So what does live rock really do for a tropical saltwater aquarium, and why is the quality of the rock so important? That is what we want to discuss with you today.


Good for Nearly All Systems


Live rock is good for nearly all saltwater tanks--whether the aquarium is a fish-only system, an invertebrate system or a full-blown reef system. One of the only systems for which live rock is inappropriate is a hospital tank. There are three primary reasons why live rock is desirable in most applications. First and foremost, live rock provides biological filtration to the system. Without live rock, the aquarist will need to provide some other form of biological filtration in order to deal with waste created by the tank s inhabitants. In addition to its role in providing biological filtration, live rock can also provide invaluable natural habitat and  biological diversity to the system.


What is Live Rock?


Before getting into too much detail, it may be useful to put forth a working definition of what live rock actually is. Despite the common name, live rock is not alive—rather it is what lives on and in the live rock that gives it its name. Live rock is porous substrate--often eroded and semifossilized coralline-covered rock--that has been colonized by flora and fauna after prolonged exposure to a biologically-rich environment. This biologically-rich environment may be the ocean, or it may be a mature closed system. In some cases, probiotics are used in attempt to speed up this process in "dead rock" or artificially-created rock. 


Most live rock on the market today comes from the rubble zones of reefs. In many cases, this rubble zone is full of pieces of living reef that have been knocked off by storm damage or other naturally occurring events. Live rock collected from rubble zones in a sustainable manner is generally a good choice for reef aquarists, as rubble zones are renewable resources. In some cases, live rock is broken off a living reef by unscrupulous collectors, and this has led to some aquarists voicing concerns about the sustainability of wild-collected rock. 


Cultured live rock is becoming more widely available and provides a good alternative to wild-collected live rock. Cultured live rock is either cultured in the ocean (mariculture) or in closed systems that already contain the flora and fauna that will colonize the substrate and turn it into live rock. In some cases the substrate to be cultured is coral rock mined from land. In other cases it is manufactured from cement or other materials. Live rock that has been allowed to dry out completely may also be used as substrate for cultured rock. If the aquarist adds “dead rock” (often sold as "base rock") to a mature saltwater aquarium, it will, in time, become live rock.


Biological Filtration


The primary benefit to using live rock in a saltwater aquarium is as a means of biological filtration. Most marine aquarists rely on a combination of mechanical, chemical and biological filtration to keep their aquaria stable and healthy. For the aquarist who does not use live rock, another biomedia must be employed (e.g. bio-balls/bales, fludized bed filters, etc.). The primary purpose of biological filtration is to convert ammonia into nitrates or nitrogen gasses. In this way, toxic waste material produced by the aquarium s inhabitants is kept in check. 


Live rock is most commonly used for biological filtration despite the fact that it is probably the least efficient bio-media available to marine aquarists. Its lack of relative efficiancy is because it possesses less surface area per pound than a biomedia such as bio balls. Having said that, it is still, in our opinion, the best biological filtration for most systems if used in sufficient quanity (one to two pounds per gallon of aquarium water). Why? Because it is the easiest to use, the most maintainence-free and it provides many benefits beyond biological filtration. Unlike other biomedia, if transported and cured properly, live rock comes to you full of life that will promote effective decomposition of organic waste in the system. 


It is possible to use less live rock than one or two pounds per gallon, if the aquarist also employs another biological filtration device such as a wet-dry, trickle filter.


Beyond Filtration


The use of live rock in a saltwater aquarium is both visually appealing and conducive to most marine organisms’ habitat requirements. Using quality live rock, makes it easy to recreate a piece of natural reef in a home aquarium. The more interesting the shape of the live rock, the more visually appealing the reef can be. Selecting a variety of shapes allows the aquarist to build caves, arches or whatever reef topography he or she is looking to recreate. Anyone watching a blenny snake between the porous passages of live rock will see that live rock is the ideal habitat.


Live rock also promotes the growth of flora that is essential to many grazing fishes health. Dwarf angelfishes, tangs and many other herbivorous fishes will do best in a tank containing mature live rock on which they can continuously graze.


Premium Live Rock  


Many aquarists will use a combination of less expensive live rock (sometimes sold as "base rock" or "boat rock") and more expensive "premium" live rock. In the case of the former, this rock may be "less alive" than the latter, or the pieces may be less interesting or less porous. The time it takes for live rock to reach the aquarists has a great deal to do with its quality, as the longer it takes, the less life survives. Rock that is flown directly from the source country is generally the best live rock, as it preserves the most amount of life. Rock that has a longer transit time due to layovers and connecting flights may still be excellent, but is not as good as rock that has flown in direct. Rock arriving by boat is generally inferior (and cheaper) but can be fully recolonized if handled properly. All live rock must be properly cured before adding fishes and other marine aquarium animals to the aquarium. 


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