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Live Rock: Some Common Questions

Especially for beginners, getting what you need for setting up a saltwater or reef aquarium can be daunting.  One of the most confusing aspects of the process may be Live Rock.  Here are some common Q & A that may make it a little clearer for anyone, especially those who just starting out.

Do I need Live Rock and what is its purpose?

Live rock is the calcium carbonate skeletons of ancient corals and other calcareous organisms, which forms the base of coral reefs.  It is not actually “alive” but is it is usually encrusted with coralline algae and inhabited by microscopic and macroscopic marine organisms.  The organisms on the live rock help to establish the biological base of the aquarium.  The rock serves as a biological filter hosting nitrifying bacteria that fuel processes like the nitrogen cycle to eliminate organic waste.  Live rock also has a stabilizing effect on the water chemistry, especially helping to maintain constant pH by releasing calcium.  The other obvious purpose is for decoration.  The rock, once established, serves as a shelter for fish and inverts, as a decorative element encrusted with colorful coralline algaes and other organisms (that may appear to spring from its surface from nothing), and as a platform for corals that you introduce to grow onto.

What is the difference between natural and cultured rock?

There are many varieties of live rock.  Most are named for the region where they are harvested, and often they have distinctive forms and characteristics. Some are dense, some are lighter and more porous, some are branchy, some are plate-like, ect.  They all basically serve the same purpose, and they may be mixed and matched according to your taste and needs.  Natural rock is chipped off and collected from specified areas in designated regions.  This rock is naturally occurring and highly variable.  Cultured rock is man-made from specially mixed concrete that is formed into basic shapes and then placed in the oceans near reefs for a period of 1-5 years where it is seeded with the same micro and macro organisms as natural rock. The rock is then collected and distributed for aquariums.  Cultured rock is favorable as it has the same benefits to the aquarium, but less environmental impact and is sustainable. It is typically less variable in shape.

How much rock do I need?

You may hear different opinions on how much rock you need, but it will depend on what your intentions are. Generally, the rule of thumb is 1-2 lbs per gallon.  This amount can vary depending on the arrangement you want and the density of the rock.  You may choose to purchase all the rock you need when setting up the tank initially, as the rock be used to cycle the tank, and will cure in the process.  Otherwise you can buy the rock a few pieces at a time, cure it in a separate vessel then add pieces periodically until the arrangement is where you like it.  The other option is to purchase base rock and cover it with fresh live rock.  Over time the base rock will be seeded by the live rock.  Just be sure your arrangement has spaces where the water can circulate through the rock and dead zones don’t occur.

What is curing and how do I cure rock?

Curing Live Rock means conditioning or cycling it for use in your aquarium. Cured rock has already been conditioned and is stable to use right away in an aquarium with minimal concern of fluctuations in water chemistry.  Fresh live rock is not cured and it shouldn’t be placed directly into a main aquarium until you cure it.  The collection and shipping process of most rock involves it being out of the water for days at a time, and a lot of the organic matter on the rock dies off.  By tanking and curing the rock, you allow the rock to recover from these stresses.  The dead matter breaks down and new beneficial organisms have the chance to re-establish and freshen up.  If you purchase fresh rock, a saltwater rinse or dip and shake will help to remove loose debris and some of the dead matter to kick start the curing process.  You can learn how to cure live rock in this short video.

How long will it take for stuff to start growing on my rock?

Once the rock is in the tank and the rest of your set-up is complete with adequate lighting, skimmer, and circulation, additives such as calcium, iodine and strontium will encourage the growth of colorful coralline algaes, and contribute to the health of other forms of live rock growth.  As the tank establishes and becomes more stable, you’ll probably see a variety of organisms from macroalgaes to small corals and other sessile inverts.  Each tank and each piece of rock may reveal different surprises, but the important thing is patience.  Taking the time for careful set-up and maintenance and a time allowance for the tank to progress at a comfortable pace will result in a healthy and sustainable reef environment.

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