THEFISHGUY.ORG REEF FORUM

Live rock does not consist of solid calcium carbonate as the hard coral skeleton is not totally solid, with spaces existing throughout the structure. These spaces are a result of the way the calcification process for the coral polyps proceeds. The base of the polyp is lifted up from the existing skeletal cup before secreting another layer of calcium carbonate, closing off a minute chamber in the skeleton. Additionally the rock is thoroughly burrowed through by boring worms, sponges and bivalves relatively quickly after the skeleton is excreted.

Any piece of rock can be turned into live rock, preferably one that consists of calcium carbonate or one that is inert and will thus not leach any undesirable elements into the system. This is achieved by placing the rock in a reef area for around 6 months. During this period organisms will populate the rock; it will become encrusted with coralline algae, populated with various worms, bacteria, crustaceans, and may even be settled by various soft and hard corals. It will then be almost indistinguishable from the 'real' thing collected from a rubble zone. Several companies are now farming live rock in this way, having sections of the sea floor covered with pieces of rock that are then harvested and sold as live rock. The good thing about this practice is that it is not removing anything from the reef directly and there is more control over the rock size and shape that is available.

Why Use Live Rock For A Reef Aquarium?
It is preferential to utilise live rock in a reef aquarium because it can fulfill three functions; biological filtration, support structure, and assist in providing a more complete and natural ecosystem.

Biological Filtration
With sufficient live rock present in a reef aquarium additional biological filtration devices, such as wet/dry filters, bio-wheels, fluidised bed filters etc, are not required. Because of the highly porous nature of the live rock then a large surface area is provided for bacteria to populate. Additionally the nitrifying bacteria (converting ammonia, NH3/NH4+, to nitrite, NO2-, and nitrate, NO3-) located on the oxygen rich external surfaces of the rock are in close proximity to the denitrifying (converting nitrate to nitrous oxide, N2O, and nitrogen, N2) located inside the oxygen poor interior of the rock. This means that there will be more efficient movement of the nutrients from the nitrifying bacteria to the denitrifying type. The additional function of denitrification is a real bonus, as this will help to keep the nitrate levels below if just a wet/dry or bio-wheel type filtration unit was used without a thick sand bed. Used in conjunction of a thick sand bed it can reduce the nitrate to very low levels and even to undetectable levels.

The amount of live rock required for a tank is a difficult thing to determine as limited exacting study has been done in this area. Currently a rule of thumb is used that 0.13 kg/lt , or 1 lb/gal, of live rock is use as a minimum. This amount is also dependent on; the density of the rock utilised (with the higher the density or the rock, then the more rock that is required), and the bio-load of the tank (with the higher the bio-load, then the more rock that is required). A better way would be to fill the aquarium with rock such that around 1/4 or more of the tank volume is occupied by the reef structure, more on this later. This will provide sufficient surface area for bacteria to grow on and room for the addition of corals and the rocks they are typically attached to.

Reef Support
Using live rock provides a perfect, natural structure for all the reef organism to live on, within and around. This is because it is actually what a reef is composed of, although on a larger and grander scale. Additionally the rock shapes obtained can be quite spectacular on their own, making a beautiful reef aquarium even before any organisms such as fish, corals, crustaceans etc are added by the aquarist.

Complex ecosystem
In order to provide a stable and 'natural' environment within a reef aquarium, it is advantages to provide as much of the natural conditions as possible. A very important natural condition that should have considerable focus is the food web and its complexity. The more organisms that are present on each of the levels and niches within the food web, then the more stable the system will be. A rough approximation to model 'ecosystem' that is in dynamic equilibrium will be attained. This may sound like a contradiction, but what this means is that the system is stable but species populations continually change around an equilibrium number.

Live rock, and live sand, provide a very simple and easy way of introducing a large variety of organism into the ecosystem. Most of them are added without the knowledge of the aquarist. It is actually the organisms that are typically not seen that are important in helping to maintain system stability. These include the worms, bacteria, isopods, copepods, and many relatively unknown interstitial fauna.

Undesirable Organisms
It must be noted too that 'undesirable' organisms can also be imported with the live rock into the aquarium. Undesirable organisms are those that cause problems with the health of the target organisms the aquarist wishes to maintain in the reef aquarium, but in nature they are in fact an important part of the entire ecosystem. These include mantis shrimps, bristle worms, crabs, Aiptasia sp. (rock anemones), Valonia sp. (bubble algae), disease causing bacteria etc. They can all be controlled and removed from the aquarium by careful and thorough procedures quite easily. Disease causing bacteria is something that will always find its way into an aquarium what ever is done, unless of course everything that is imported into the aquarium is disinfected, even the fish and corals. The good thing here is that diseases are never a problem in a healthy, stress free tank with health inhabitants. Most are diseases are opportunistic in origin, so if the fish or coral is stressed and has a weakened immune system then disease is likely in some form or another can grab a hold and cause havoc with the animals health. These negatives, though, are vastly outweighed by the positives of utilising live rock in a reef aquarium.

What Is Cycling Of Live Rock?
Typically after live rock is collected from a reef rubble area, it has to be transported to a dealer, an aquarium store, and then finally to the aquarists. The problem is that during each of the transportation or storage periods less than ideal conditions are provided for the live rock. Many of the organisms become unduly stressed by stewing in their own wastes for extended periods and lack of light. It is likely that many will even die. Additionally there are species that cannot even survive within a reef aquarium for various reasons. Cycling allows the dying animals and plants contained on the rock to die off and the resulting products from the decay of the tissue to be further processed into relatively harmless compounds.

The cycling period gives an aquarist an opportunity to see evidence of the ammonia cycle, or nitrification which is the conversion of ammonia to nitrate. During this cycling period the ammonia level rapidly climbs as heterotrophic bacteria process the dead organisms. This high level of ammonia, with ammonia being toxic to most marine organisms, can have a synergistic effect and cause more organisms to die. Which will then in turn produce more ammonia. The populations of bacteria involved in the converting ammonia to nitrite quickly build up to sufficient numbers to process the waste generated and the ammonia levels go down to undetectable levels (by aquarist test kits). Nitrite then becomes the dominant toxic species present, which another group of bacteria feed on and convert to nitrate. The nitrite to nitrate bacteria take a bit longer to build up a sufficient population to handle the waste, but then the nitrite levels will become undetectable by aquarist test kits. This is the important part at this point but later denitrification can start and remove the nitrate which starts to increase in concentration.

It is possible to buy live rock cycled, partially cycled or almost straight from the reef. If the live rock is going to be utilised in an existing reef aquarium then cycled live rock should be used. This will minimise the peak in ammonia and nitrite caused by the addition of the rock to the system as there will be very little die off. In a well maintained tank it is even possible to add some additional live rock to the system without any visible adverse effect to the inhabitants. It is preferable to cycle the live rock in the target aquarium, not in the collectors, dealers or aquarium stores tanks. What this will allow is; greater control over the cycling period, the possibility of more organisms surviving this highly stressful period, and minimise the loss of mobile organisms that can leave the rock. How this can be done is discussed in the following section.

How Do You Cycle Live Rock?
The current general procedure for cycling live rock is to throw it into a large container, either the target aquarium or a large cycling tank, have a skimmer operating on the system, add large amounts of circulation and provide no lighting. It is left there for about 2-4 weeks and the ammonia and nitrite levels are monitored. The circulation is required to allow good nutrient and waste exchange between the live rock and the water, to assist in the removal of any dying organisms from the rocks, and to minimise any areas that may go anaerobic. Areas may become anaerobic because of a large organism dying and the large oxygen usage by the bacteria processing the tissue. No lighting is provided to avoid any excessive micro algae blooms in the system while nutrients are at an elevated level. The length of the cycle takes around 2-4 weeks, from the time the rock is placed in the vessel to when the nitrite levels drop to undetectable levels. Longer periods are possible, and in some rare cases the cycle seems to get stuck after the ammonia levels drop. The reason for this is still unclear, but may have something to do with inhibitors for the nitrite to nitrate bacteria (which are more sensitive to environmental conditions and slower growing than the ammonia to nitrite bacteria) being introduced into the system via some mechanism.

The 'dark' technique of cycling of live rock is seen by the author as an out of date technique. It really should be avoided because there is no effort made to make the cycling period less stressful for any of the organisms present. There is a much better way to do it which will provide a higher survival rate. The idea is to; provide enough light to photosynthetic organisms such that they can survive and low enough such that micro algae cannot bloom during this period of high nutrient levels, and remove as much of the waste from the system before it becomes converted into a pollutant or remove the pollutant from the system.

The best type of lighting to use is actinic as it is typically of the correct wattage and it supplies directly the wavelength ranges that the photosynthetic organisms utilise. So far as a rule of thumb around 0.14 W/lt (1 W/gal) is a sufficient level to use. The lights are operated on an increasing length of time during the cycling period, starting at around 6 hours per day, then increasing an hour every couple of days until the full day length is reached. Note that this is based on the authors own experience and that of another aquarists using this technique that the author has communicated with. Further experimentation in this area could be done to further clarify this, but in the cases where it has been use there has been a good survival. Once the cycling is over, then the other lighting can then be gradually phased in. Need to avoid any sudden addition of light as this will stress any photosynthetic organism as they take time to adjust to new lighting levels.

In addition to the lighting used, continuous operation of a skimmer, activated carbon, and regular water changes should be implemented. These activities are used with the idea of transporting as much of the waste and pollutants from the water, therefore reducing stress in the system. The use of the skimmer and activated carbon removes compounds before they can be broken down by the heterotrophic bacteria. Water changes remove compounds before they can break down, but also remove some of the toxic ammonia, nitrite and other pollutants from the system. There is no reason to worry about substantially prolonging the cycling period by using water changes because the amount of nutrients for the bacteria has been reduced. This is a myth. Bacteria will grow and multiply at a exponential rate, with all environmental factors staying constant, until there is a high enough population to process all of the available nutrients. At this point the population will stablise. A change in the nutrient level, which will change the end population required, will make a very small change in the time frame required to reach this point because of the exponential growth rate Additionally at the end of the cycling period, all of the dead organisms have been processed so there is now a reduced amount of nutrients available. The bacteria population will adjust to the level to process the amount of nutrients now being generated in the system by living organisms. This will most likely result in a reduction in the population from a peak during the cycling period. There is no way that initially an operating system will generate as much nutrients as is generated during the cycling period. Therefore reducing the amount of waste and nutrients will not influence the final bacteria population or the time frame to any large extent.

The recommend method of cycling live rock is summarised as follows:

*As the live rock is unpacked remove any white, slimy areas and anything else that is decaying. The white spots where an organism, typically a soft coral, hard coral or sponge, has died. Removal will help to minimise the stress on the system by removing another source of nutrients.
*Clean off some of the invertebrates on the rock, such as sponges and corals. But unless you know what you are removing and are experienced they you may remove some very valuable specimens. There is no need to be so harsh and take to it with a brush and scrub it clean. This practice is rather excessive.
*Inspect each rock for the presence of bristle worms and remove any if found. Bristle worms have a tendency to come out of the rock, or hang partially out, after the rock has been in transit.
*It is a good idea to remove any plant growth, both macro and micro algae, as these can easily re-grow from the root system left behind.
*Arrange the live rock in the aquarium. Ensure that only small areas are in contact with the bottom of the aquarium and between the rocks. This will ensure good water circulation around the reef structure. Working towards small contact areas between the rocks also helps to build an open reef structure with many tunnels, arches, overhangs and caves. This has the added bonus of making a much more interesting reef structure to look at and arrange inhabitants on.
*Position return and circulation pump outlets such that there is good water movement throughout the entire reef structure. In dead spots detritus will accumulate. This can be use to an advantage by making a spot where detritus can settle that is easy to access. Then regularly the detritus can be siphoned out of the system.
*A mechanical filter can be used during this period to help remove suspended solids from the system, but ensure that it is cleaned regularly, every day is preferred. This is because the material the filter catches is not removed from the system. It will continue to break down and contribute to the addition of pollutants in the system.
*Operate the skimmer continuously and tune such that a dry, dark foam is collected.
*Keep activated carbon in a high flow area of the system such that the water passes through it. Once the cycle is over use activated carbon as usual, whether intermittently or continuous.
*Operate the actinic lighting from the beginning, starting with about a 6 hour photo-period. Gradually increase this by an hour every couple of days until the full day length of 12-14 hours is attained.
*If white spots appear on the rock or something appears to be dying then siphon or remove it from the rock.
*Regularly perform partial water changes and siphon out any detritus that has settled anywhere in the system. The more frequent these water changes the better, as this helps to keep the levels more constant without giving huge swings. The amount of the water change can vary, but a 50% is a good start. If there are problems with such a high volume change then decrease to a level that is possible. But the higher the water change the better as it will remove more of the nutrients and pollutants.
*When the cycling period is over, with ammonia and nitrite levels undetectable, start to phase in the main system lights. Do this gradually to reduce stress on the photosynthetic organisms present and to avoid a micro algae bloom.
*Start a regular maintenance program, including water changes at the length and volume for a normal operating system. This varies, but around 5-10% of the system volume per month is currently recommend. But higher and lower levels have been successfully used by various aquarists.

Live Rock Usage In A Reef Aquarium

Just a couple of points to be considered when using and arranging live rock in a reef aquarium:

*Quality is important, especially for the pieces that will be in full view. Those with good shape and coralline algae growth are worth the extra expenditure for center pieces.
*Do not have to have the same quality of live rock through out the aquarium. With a larger tank it can be quite easy to use lower quality for the base of the reef structure and then more expensive for the sections of the reef that will be visible. This will help to keep the expense involved down a bit. Can even use just a type of inert rock for the base as this will quickly become populated by life once in a system with live rock.
*Good circulation is important. This allows for good nutrient and waste exchange between the rock and the water.
*Arrange the rock in a lightly packed open structure, allowing water to circulate freely through the rock. This will create many little tunnels, caves, arches, and overhangs throughout the reef structure.
*Have only point contacts between the rocks to minimise dead zones or points where detritus may accumulate.
*Avoid detritus settling zones is possible. Although these are not that bad, as many organisms live in this sort of environment. But keep them to a minimum.
*Better if don't lean the rock against any part of the aquarium walls, as this allows for better circulation.

Bibliography:
Delbeek J.C., and Sprung J., The reef aquarium: a comprehensive guide to the identification and care of tropical marine invertebrates, vol. 1, Richordea:Coconut Grove, 1995.
Moe Martin A. Jr., The marine aquarium reference: systems and invertebrates, revised ed., Green Turtle:Plantation, 1993.
Ruppert Edward E., and Barnes Robert D., Invertibrate Zoology, Sanders College:Sydney, 1994.