The major bio-filtration media in use by marine aquarists, whether they keep a reef or fish only system, is probably live rock and for good reason.
Premium live rock is rock that has been fairly recently harvested from around the reefs, meaning it is ‘rubble’ rather than hewed from the reef itself. This rock has growths of all sorts which could be of interest to the aquarist. Unfortunately, live rock needs to be cured after import which simply means that all the dead and dying organisms on and in the rock have to be removed, meaning that pollution will not occur in the aquarium. However, for the most part there are tougher organisms that do survive and they could make an appearance in the aquarium, this appearance could be months after the rock has been introduced. Live rock can also harbor unwelcome organisms, such as the aquarium weed aiptasia, an anemone that could become a real nuisance without controlling attention.
In addition to natural organism introductions with the rock, it is very decorative. Reef and fish only aquarists are able to construct a very interesting and decorative structure which suits livestock very well.
The next great attribute of live rock is mentioned in the first paragraph – bio-filtration. Living organisms in the aquarium will literally be poisoned unless there is some means of negating the toxic substances that they produce. The two major toxins are ammonia and nitrite, and a much less dangerous one is nitrate. Dwelling on and in the live rock are oxygen requiring bacteria which convert the toxin ammonia to the toxin nitrite, which is then converted to nitrate. Bacteria living within the rock also require oxygen but find it hard to obtain, therefore they extract it from the nitrate which breaks the nitrate down releasing the residue from the aquarium as gas. The process from ammonia to gas release is known as the nitrogen cycle.
Live rock is a great commodity for the aquarist, providing the major and essential job of bio-filtration and also doubling up as decoration. The rock must of course be present in sufficient quantity to deal with the bio-load present, which is created mainly by fish.
There’s only one problem and that is cost, it’s expensive, particularly the premium grade. It’s expensive to air freight rock. This cost could be controlled up to a point by using base rock as the lower part of the rock structure and premium grade for the surface – but it is still expensive.
One way of avoiding this cost is to create live rock, which isn’t difficult. What is required is inert porous rock, that is, rock that is known to be free of any substance that could be harmful in seawater and also porous. This type of rock is often available in local fish shops and at a very much lower cost than the live variety. It isn’t any use purchasing solid non-porous rock. The second requirement is that there needs to be as much rock as would be used if the live variety were bought, which should ensure that the amount of bio-filtration media will be adequate.
If necessary the rock is thoroughly rinsed before it is placed in the aquarium to form a structure as required. The aquarium is then filled with seawater (note the net gallonage for future use) at the required specific gravity (SG) and heated to the design temperature. Seawater circulation should also be turned on. At this stage there isn’t any need for lighting. The seawater should be left to settle down to the required parameters. Check the seawater SG once it has heated up as temperature could affect it.
Once the seawater is at the required SG and temperature attention can be given to processing the rock. Anyone who has ever used a canister filter for bio-filtration will be aware of the process. A commercial maturation fluid is obtained and added to the seawater at the amounts given in the instructions. Test kits for ammonia and nitrite are also required, and the seawater should be tested in accordance with the instructions. Eventually the ammonia reading will disappear, followed by the nitrite reading. Once the aquarist is sure the reading remains at zero for both, the rock can be considered to be initially mature, that is, there is an initial population of bacteria to deal with toxins.
A test should now be done for nitrate; a level will probably be clearly seen. This nitrate should be reduced by a seawater change until it is as low as possible or preferably undetectable.
Slow stocking can now commence, turning the lighting system on of course. It is important that ammonia and nitrite tests continue, if there is any indication of either ammonia or nitrite stocking should cease until the reading(s) are zero again and remain so. The bacteria need to adapt to the increasing bio-load and must be allowed the time to do so.
Eventually of course the aquarium will be stocked as required. The bacteria population is able to stabilize and after a further say three months can be considered as fully mature. Routine seawater changes, as with any system, need to continue as does testing.
Wait a minute though; we’re supposed to be creating live rock which should be able within reason to deal with nitrate. So it will, in time. It takes longer for the nitrate reducing bacteria population to establish, and once it has the nitrate should be controlled. Relative to live rock and nitrate what does ‘within reason’ mean? It simply means that if the aquarium is often overfed and the toxin reducing bacteria produce a lot of nitrate, and the aquarist is missing routine seawater changes, the nitrate could be too high for the bacteria to control.
Ok, so now we have an aquarium filtered by live rock. What about the natural growths that could occur (though not always) with natural live rock? These will obviously be absent as the rock was initially dead. With both the fish only and reef system, if the environment is of high quality it shouldn’t be long before encrusting algae’s make an appearance. In a fish only system it could be necessary to seed with a small piece of rock from a friend’s aquarium that already has encrusting algae on it. In a reef system, when the aquarist introduces corals they will usually be attached to pieces of natural rock. These rocks should contain organisms that should seed the other rocks provided a high quality environment is maintained. Before long the previously dead rocks should look completely different – just like natural live rock.
So for a considerably reduced price live rock is achievable. What the aquarist needs to provide is some patience (required by all marine aquarists) and considerably less money. There is great concern about the future of the wild reefs and concern has been expressed about the impact of live rock collection, so the aquarist who produces his/her own will be assisting with reef protection.