Live Rock for Saltwater Aquariums

Technically speaking, live rock is any porous rock colonized with life after exposure to a biologically rich environment. The biologically rich environment is usually a natural reef, and the rock itself is usually rubble that has been knocked off a living reef by storm damage. Live rock is also aquacultured in some places, although it has yet to be determined whether this process will catch on with consumers. Like aquaculture, “dead” rock (sometimes sold as “base rock”) introduced to a mature marine tank will become “live” over time as it is colonized by bacteria and other organisms.

Because live rock is full of life, it should be treated as a living thing. This means that after purchasing live rock at the local fish store, you should take care to keep it wet (wet newspaper draped over it in a cooler works fine for short trips), oxygenated and warm (between 70 and 80 degrees F). If you purchase live rock online, be sure it is packaged properly and shipped quickly.

Even under the best conditions, some of the flora and fauna growing on the rock will be damaged and will eventually die. This is why live rock needs to be “cured.” If the aquarist purchased so-called “cured” live rock, the curing period in the hobbyist’s tank will be much shorter than if he or she purchased uncured live rock. The process of curing live rock simply refers to the dying-off of organisms damaged during transport, and the resulting chemical byproduct of this die-off—ammonia. During the curing process, no other organisms should be added to the tank, as the toxic levels of ammonia will likely kill anything but the hardiest animal.

Once the live rock has been cured (identified by water testing) and the desired aquascaping is complete, the aquarist should do his or her best to not disturb the rock. It is essential to allow the exterior surface to be fully colonized by denitrifying bacteria. Live rock, bacteria if used in sufficient quantities, will serve as an excellent biological filter when colonized by denitrifying.

If the aquarist plans to use live rock as the system’s sole biological filtration, at least one pound of live rock per gallon of water should be added to the tank. Many aquarists add as much as two pounds of live rock per gallon—an expensive proposition when premium live rock sells for upwards of $4 per pound. One trick is to buy a combination of much cheaper “base rock” and more expensive live rock. The base rock can then be used to build the shape of the reef structure, and the live rock can be added around and on top of the base rock for its aesthetic value. The base rock will, of course, take longer to be colonized than the live rock.

Alternatively, the aquarist can use a smaller amount of live rock in the display tank and then employ another biological filtration system in the sump (such as a wet-dry, trickle filter) or adjacent to the tank (like a fluidized bed filter). Regardless of whether or not the aquarist chooses to use live rock in quantities sufficient to handle all biological filtration, the live rock should be a part of every saltwater system including fish-only systems.

Why You Should Use Live Rock

Live Rock as Habitat

The use of live rock is both visually appealing and conducive to most marine organisms’ habitat requirements. It is easy to recreate a piece of a natural reef in a home aquarium using live rock. The interesting shapes provide myriad opportunities to build caves, arches, or whatever reef topography you are looking to recreate, and these features—built out of live rock—are the most similar to the tank inhabitants’ natural ecosystem. Anyone watching a blenny snake between the porous passages of the rock will see that live rock is the ideal habitat.

Live Rock as Bio-Media

In terms of biological filtration—one of the three types of filtration upon which most marine systems rely—live rock is an excellent choice if used in sufficient quantities (one to two pounds per gallon). In short, live rock is very porous resulting in lots of surface area, and biological filtration is all about surface area. It is this surface area that is colonized by denitrifying bacterial fauna and which is largely responsible for the effective decomposition of organic waste in the system. It should be noted that live rock, when compared with other bio-media, is the least efficient given its weight to surface area ratio. Nonetheless, live rock’s other attributes, combined with its utility as bio-media, make its inefficiency pale in comparison to the benefits.

Live Rock Contributes Biological Diversity

There are so many times during the set-up of a marine aquarium where the aquarist must wait for days, weeks or months before adding the next animal to their tank. Studying the remarkable biological diversity which comes free of charge on healthy live rock, makes this waiting period a whole lot more interesting. Break out your magnifying glass, and sit close to the tank. You will be amazed at the diversity of species that “come to life.” From sponges and peanut worms to various mollusks and echinoderms (serpent and brittle stars), the organisms that give live rock its name will no doubt amaze the viewer, and their diversity will contribute greatly to the overall stability of the system.

Some Quick Facts about Live Rock

  • Much of the available live rock is eroded/semifossilized coralline rock.
  • Lee Chin Eng, an aquarist from Jakarta, is often considered the father of live rock (which he called “reborn coral”).
  • Base rock is cheaper than live rock, and a combination of base rock and live rock is therefore more economical. Over time, it will all become live rock.
  • It’s possible to use less live rock, and employ another biological filtration device such as a wet-dry, trickle filter.

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