'Living rock' might sound like a strange thing to a non-marine fish keeper, but it is an essential part of any reef aquarium and plays a vital role in creating a healthy environment for corals and some reef fish.
What is live rock?Live rock is porous rock that contains many tiny organisms including algae's, bacteria, sponges, and tiny creatures just visible to the eye. At first glance, live rock can look just like normal, established rock, but the organisms it contains means it has a direct effect on the aquarium water and its chemistry, hence the term 'live rock'. Because live rock is collected from the oceans and transported from tropical regions such as the Fijian Islands, it carries quite a considerable cost in air-freight and storage. It often comes as a shock to new marine fish keepers that you may have to spend well over a hundred pounds on some rock for your tank!
How does it affect the tank?The organisms within live rock will help to break down larger waste particles that get trapped in the rock, but more importantly they will also break down pollutants in the water, including nitrates, which needs to be kept at low levels for your corals and fish. In addition, the live rock is a home for thousands of tiny creatures that will hopefully breed and provide a continual supply of food for more picky fish, and also for some corals. Live rock can be useful in non-reef marine tanks but it is not essential and will only thrive under bright lighting. To get the best results from live rock in a reef tank you should have as much as possible, but ideally at least a quarter of your overall rock should be live rock.
Cured or un-cured?Because live rock is a home for many organisms and also holds trapped waste material, transporting it around and exposing it to changes in temperature and salinity can result in some of the organisms perishing, which is often called 'dieback'. When dieback happens, the live rock can release pollutants (most notably ammonia) into the aquarium before the remaining organisms recover and re-grow to fill the areas left by those that have died. 'Cured' live rock is rock held by your retailer that has been cleaned and settled to remove dieback and minimise the chance of any more significant dieback when the rock is transported to your aquarium. Uncured live rock has not had this settling period and is likely to produce significant dieback when introduced to your tank
Why use uncured live rock?Dieback from uncured live rock will pollute the aquarium and raise ammonia levels, which would normally be considered a bad thing and something to avoid. The type of pollution and waste created from uncured live rock however, is ideal for seeding, cycling, and maturing a new aquarium before fish, inverts, or corals are added. To cycle a tank using live rock you should add the rock in stages over several weeks and keep a close check on water conditions; allow ammonia and nitrites to rise slightly and when they fall add more rock to repeat the process until you have all the rock you require. You can add cured rock to the tank once fish and inverts are established, but you should treat the rock as an item of livestock and only add a piece at a time.