[Maryrosi]

Live Rock and Its Use in Marine Aquaria, Part 1
by Mike Paletta

After understanding the nitrogen cycle, nothing has advanced the marine hobby as much as the use of live rock for biological filtration. Prior to the use of live rock, most marine tanks consisted of dead coral skeletons sitting on a white bed of dolomite along with an undergravel filter; which is where biological filtration took place. With the introduction of live rock, not only was a more natural looking environment provided but the locus of biological filtration was shifted as well. This has increased the likelihood of success in the hobby many fold.

The term "live rock" seems to be a misnomer in that terrestrial rock certainly is not alive. The mineral portion of live rock is indeed not alive. In fact, it is not even true rock: it did not form as a function of the earth's mantle cooling. Rather, the rock portion of live rock are the dead coral skeletons from the reef that have broken off from the coral reef itself and become worn down and mineralized over time. These fragments have then been colonized by bacteria, algae, sponges, etc. that create a living patina on the rock. However, these organisms are not restricted to colonize only the surface of the rock. Many of these organisms bore into the rock itself and consequently live on the innermost surfaces within the rock structure. For this reason, not only can live rock act as the substrate for common aerobic bacteria, but it can also act as a culturing ground for the anaerobic and anoxic bacteria that live within the inner spaces of the live rock: which can help to reduce nitrate to some degree. This is also why some organisms, such as boring sponges, may live deep within the rock's surface: when these organisms die, it can take a long time for them to completely decompose be removed. Some algae may be problematic on certain rocks for an extended period of time even though the surface of the rock appears clean and does not have seem to any source of nutrients to fuel the algae's growth.

The nature of the rock itself also makes it different from most rock. If you look at virtually any terrestrial rock, what you see is something completely solid with the surface area being restricted to what you see. Live rock is quite different due to how it is formed. As a result of being constructed by tiny colonial coral animals, live rock is full of nooks and crannies that can be as large as your finger or a fine as a strand of hair. All these interstices, coupled with the boring animals, provide this rock with tremendously high surface area. This large surface area, which is almost completely colonized by bacteria, allows live rock to be the only substrate necessary for biological filtration in some reef systems.

As a result of the use of live rock, an entire industry has arisen to provide the consumer with this necessary component of a successful reef tank. This proliferation of collectors, collecting methods and storage methods has led to a lot of questions regarding the qualities of live rock. The most frequently asked question concerns the differences between "cured" and "uncured" or "fresh" live rock. Almost all live rock is harvested from the ocean and shipped moist to the dealer or hobbyist. It is shipped this way to reduce the large freight cost that would occur if it were shipped under water. In this state, it is "uncured" or "fresh". As a result of this moist shipping method, many of the organisms present on the rock die off and release a lot of organics into the water. Once this die off has ceased and the organisms have stabilized, this rock is considered cured. Some dealers have holding facilities to cure this rock. However, due to the premium price charged for this rock, it is often more cost effective to cure one's own rock. Also, even though the rock may be cured in a wholesale facility, the stress of shipping it, even if it is only a short distance, causes some die off so it will need to be cured again once it reaches its final destination.

The curing of the rock is not too difficult. As long as adequate time is allowed for the curing, there should be very few problems. I have been using the same curing method for the past fifteen years with good results. Upon arrival of the rock, it should be rinsed in a saltwater bath of appropriate salinity and temperature. This is done in order to remove any detritus that has settled on it as well as to remove any grossly dead organisms. Upon completion of the rinse, the live rock should be inspected and any dead or unwanted organisms (bristle worms, algae, chicken liver sponge, etc.) removed with forceps or tweezers. Dead organisms are usually readily apparent by their white color, limp structure or offensive smell. I strongly advise removing any sponges that are growing on the rock even if they appear to be alive. Sponges can cause the most fouling during the curing process. This is necessary as sponges that have been exposed to air for any length of time usually die as a result of the system not having a means for removing air that has gotten trapped in their tissues. So even though they appear alive, they are already dying due to this exposure. Also sponges tend to die slowly, so while they may appear alive on the rock, they are in the process of dying and could release organics into the water for an extended period of time. The worst offender on this account is the chicken liver sponge. This black or dark brown sponge encrusts a lot of the live rock that comes out of Florida and the Caribbean. If not removed promptly, this sponge will die over several months releasing organics the entire time. It is best to remove any fragment of this sponge. All of the macro algae should also be plucked from the rock as well. Not only will most of the algae die from the trip, releasing nutrients, but what is left will also grow profusely due to this excess of nutrients.

After all the undesirable components have been removed, the rock should be placed in the aquarium that will eventually be its home. It should be placed close to the pattern that it will eventually rest in. How the live rock should be placed will be discussed below. The water should have been in the tank for a week or longer prior to the addition of the live rock. This is done to reduce the negative effects caused by the caustic nature of freshly prepared seawater. All of the rock should be cured at once as it is very deleterious to an established reef tank to add new uncured rock to it. Even rock that has been cured in a separate system has the capacity to dump a lot of nutrients into an established tank, so this should be avoided.

While the rock is curing, two important things need to be done. First, strong water movement on the rock is essential. By providing strong water movement, any material that dies will be blown off the rock. In addition, strong water movement will prevent detritus from settling on the rock and killing whatever that is underneath it. To produce this water movement, using multiple powerheads will work well. To augment the water movement, it is often necessary to use a bulb baster to remove some of the white film that invariably forms on some of the live rock that is away from where strong water movement is occurring. Second, good protein skimmer is an important factor for proper curing of the live rock. Using a good protein skimmer aids in curing the live rock in that much of the dead material is skimmed away before it can pollute the tank. In addition, the skimmer adds oxygen to the water so that anaerobic conditions do not develop.

For the first week to ten days, the lights should remain off. After this initial period, the lights can be turned on for less time than would be the normal photoperiod. The goal is to provide enough light for the coralline algae to grow but not enough to stimulate nuisance micro algae growth. After this 4-6 week curing period, the light duration and intensity can be increased to normal levels.

During the curing process, the only substances that may be added to the tank are calcium, magnesium and strontium. These substances are added during the curing process to try and give the calcareous algae an advantage. If these substances are not in adequate supply, the coralline and other calcareous algae will tend to die off. As a result, the less desirable micro algae will tend to overtake the rock. However, if the water used to cure the rock is newly prepared, there should be adequate amounts of these elements present so they may not need to be supplemented.

The amount of coralline algae present on the rock is dependent upon from where the rock was taken. There are many types of live rock available including: turf rock, base rock, rubble rock, worm rock, or reef rock. Each of these rock types have different characteristics as a result of where they were harvested. The characteristics of the rock also differ as a result of which body of water the rock was taken from.