Live rock is an excellent tool in the aquarium if used carefully. Most commercial liverock is imported from Fiji. Live rock is almost always based on coral skeletons or any calcium-rich, soft rock. It grows various algae species, which both helps enrich the water quality and gives fish such as tangs something to graze on. It also frequently has small marine life such as crabs, baby starfish, tiny clams and other mollusks, tuberworms, tough coral polyps, and occasionally "macro algae (bushy green growths that most people mistake for seaweed) and occasionally true seaweed species, although most of these marine plants soon die in a tank enviornment. This also provides an excellent base on which to place anemonaes and showy live corals.

The most important thing about live rock is the bacteria, however. The rock is by nature soft and poreus, providing many many places for bacteria species to lurk and thrive. These bacteria are benificial to a tank, providing biological filtration, helping the tank through the nitrogen cycle when being established and keeping the tank toxin-free in an older aquarium. But unless you are very experienced, it is suggested you NOT use live rock to establish an aquarium. A tank with just an adequate wet-dry filter takes roughly 6 to 8 weeks to cycle correctly, with a water test at least once a week to test while ammonia, nitrite and nitrade rise and fall before stabelizing. While adding live rock cuts down on this time, it makes it nearly impossible to test for. Ammonia may show up from decaying matter on the rock, the tank may be able to remove nitrite sooner than expected with a small fish load, due to the presence of the extra bacteria. But once more fish are added the tank very often becomes unstable and you lose pricey animals. It is generally recommended (to the novice at least) to cycle the tank completely with sand and pure coral skeleton and rock, adding live rock on top of this only after the cycle is complete. Many people will cycle properly for 6-8 weeks with damselfish (see saltwater aquarium for information on how to cycle), THEN add live rock, then wait another week or so before adding valuable fish to the tank (and only the heartier species at first, at that).

Generally, one pound of liverock per gallon of water is just about perfect. Most people will build up a framework of rock and put liverock only as a "top" layer, for a reef look. If all liverock is used, most of the material near the inside will not recieve the light, nutrients, or water circulation it needs and will die off and pollute your tank (not to mention cost you extra money), whereas with a skeleton in place, the organisms off the liverock will multiply and spread to previously 'dead' rock in good growing conditions. The organisms on liverock will also spread to sand or crushed coral gravel in time, yielding live sand as well.

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