Filtration is required in the aquarium to prevent a build-up of the toxic chemicals that arise from organic waste and decay. Tank water can be filtered either artificially (with appropriate equipment and periodic replacement of chemical adsorption media), or biologically - replicating natural processes and cycles within the aquarium: this method is just one function of what aquarists refer to as 'Live rock', but the following covers every aspect of this fascinating material. (Note that all aquaria require proper water circulation and aeration regardless of the filtration system).
The Functions of Live Rock in the Marine AquariumFirstly, a sufficient quantity of live rock, together with the protein-skimmer (foam fractionator), will answer all the filtration requirements of the tank. Live rock is porous and sustains two sorts of useful bacteria, one sort involved in aerobic breakdown of waste near the rock surface, and the other in anaerobic breakdown (nitrate elimination) deep in the rock's interior:- the greater porosity of the rock, the greater this contribution to the aquarium's ecosystem. The amount needed depends on the population of the tank, type of rock, surface area, etc., but a usage of 1kg per 7-8 litres of water, or around one quarter by volume - as little as 1kg per 15 litres using Aragite - is quite typical. (Weight criteria alone could be met using a denser rock, but this is often more impervious and less effective as a bio-filter). Note that in a live-rock system, detritus and particulate matter is managed - and required - by scavengers such as smaller fish, crustaceans, snails, sponges, worms and other inverts, and the use of mechanical/particle filtration is only necessary if this range of filtering-organisms is depleted or absent.
Secondly, live rock acts as a base or anchorage for individual organisms, in particular, anenomes and the all-important coralline algae (see below).
Thirdly, live rock acts as a habitat and haven for the free-swimming creatures of the aquarium. The welfare of individual fish in the tank is paramount:- besides water quality, lighting and feeding, the other factor over which the aquarist has any control and which is most likely to affect the longevity of the livestock is stress. Most fish react very badly to changes in their environment or inappropriate physical conditions, and are much more susceptible to disease and the attentions of opportunistic organisms (including other fish) when they are distressed - partly because they stop feeding properly. The sanctuary afforded by rocks, reef structures, etc., is crucial to their welfare - this is especially so for new arrivals in the tank, who immediately need somewhere secure while they acclimatize. In the longer term, the interest and amusement value of a reef structure adds as much to the contentment of the fish as it does to the observer!
Fourthly, the presence of rocks particularly when arranged to provide a combination of reef wall, shelf and some bedrock, greatly extends the range of feeding conditions, so that the fish can graze or pluck food from different situations, and do not have to compete for food at the same point in the tank.
Lastly, the object of the reef aquarium is to emulate as closely as possible the ideal underwater scene. Besides enabling the viewer to see the fish at their very best, everyone's perception of the perfect underwater world includes that magical reef wall.
Natural RockLive rock can be obtained from any of the warmer seas of the world; it usually has a high calcium content, being largely formed from the fossilized skeletal remains of creatures that died millions of years ago. Ideally, the rock will be very porous (porosity is directly related to bio-filter capacity) and have good encrustations of coralline algae. The characteristics of natural rock vary greatly according to origin; the principles sources are the South Pacific islands, the Indian Ocean and the Caribbean - the rock from this latter area tends to be more slab-like, and lends itself better to reef wall construction. The branched 'rock' from Fiji and Tonga, etc. is not rock in the true sense but coral skeleton; it is quite dense/non-porous and therefore has mostly decorative value. Live rock should be distinguished from Ocean rock; although much cheaper, the latter is just solid, impervious rock - with no bio-filter value.
Natural rock is cleaned and cured for many months so that the harmful and more vigorous organisms are eliminated. The rock is exported in a moisture-retaining packing (i.e. not actually in water, as the extra weight would make shipping prohibitively expensive); on arrival here, the rock is immediately re-immersed. In favourable conditions, coralline algae will rapidly colonize or 'encrust' bare rock (in the preparation process live rock is sometimes completely re-seeded with 'cultivated' algae).
Although natural rock has the advantage of being ready-made, it does have drawbacks - most notably cost - and the trend is towards using the more efficient and versatile reconstructed rock (See Aragite and Maragic below).
It is possible to achieve bio-filtration with live sand (bio sand), but this requires a bed of around 100mm depth; as it is essential to prevent the settlement of detritus that might reduce the effective surface area, a mechanical filter is also required. Since it is desirable to have a quantity of rock in the tank for the reasons cited above, live rock is usually the preferred solution - unless the type of livestock necessitates a large volume of sand; nonetheless, a reef structure rising out of a bed of golden sand can be very impressive (a well-cleaned, acid-free bulding-sand is fine); some of the sand can be siphoned off with water changes to keep it pristine - leaving a stratum of sand that will become 'live' anyway! (Switch off pumps before adding the sand, and pour down a pipe to avoid clouding the water).
Aragite & Maragic Live RockBio-filtration is self-sustaining and maintenance-free, but the cost of enough natural rock to answer the filtration needs of a 55 gallon aquarium - and create an attractive reef - can be substantial; moreover, the size and shape of the individual rock pieces are not usually ideal for constructing a stable reef structure, and often result in wastage and 'dead areas' (zones with inadequate water circulation); furthermore, naturally-occurring rock is not actually designed to act as a bio-filter! Fortunately, alternative materials are available which are far more economic and efficient, and are extremely versatile in the shapes and sizes of rock that can be produced.
Aragite is a calcium-rich material which is mixed with water and sets into a highly-porous rock; weight for weight, its bio-filter action is at least twice that of natural live rock. Aragite passes through several distinct stages during setting; initially, it can be moulded or poured, but its consistency changes within a few minutes, and it can then be 'dolloped', sliced or shaped - rather like cheesecake; chunks can be drawn out, or torn off and re-attached; with the use of a table knife, more-exotic shapes can be made by folding the material over on itself to form caves, niches and shelves, etc*. A reef or rockscape can be built up with a greater filtering capacity, and no wastage or possibility of introducing infections, etc; being less dense, rock features can be built up using a lesser mass of material. Aragite naturally acquires a rocky appearance on drying and enough rock for a 55-gallon tank (in an assortment of shapes and sizes) takes just 2 - 3 hours to cast. It usually takes a few weeks for coralline to become fully established. Curing period: 3 days.
Maragic is a slightly less porous material (and consequently has a lower filtration coefficient) but it is suitable for both fresh and saltwater aquariums; in all other respects it is formed and handled in the same way as Aragite.
We despatch a coralline seeding & microbe booster pack with each order, but do note that desirable naturally-occurring bacteria are always present anyway: the bacteria will take a short while to colonise the newly-made rock, so it is important not to overpopulate the aquarium during the initial 2 or 3 weeks. If you are converting from artificial filtration, the changeover should be phased in over 2 - 3 weeks, and any UV filtration left off for 4 - 6 weeks. The coralline spores will take hold on the new rock very rapidly (Coralline spores will almost certainly be present in the tank, in any case).
*A reef wall can be built monolithically or in sections, adding any prominences, recesses, caves, etc., while the material is semi-set (the material remains 'sculptable' after curing). Aragite may also be used as a jointing material. (Instructions are included).
About CorallineEncrusting coralline algae (pseudolithophyllum, the type of interest to the aquarist) is the pink, red or purple patchwork that forms on rocks etc., and is important for several reasons. Firstly, the algae produces chemicals that nurture the herbivorous invertebrates in the tank; these help to suppress the growth of other plants - including stemmed algae - which would otherwise smother the reef system, or block out light. Secondly, at the microscopic level, the algae has a matted structure, so the encrustation forms a stabilizing layer across the reef/rock arrangement. Thirdly, coralline algae and fish thrive in the same conditions of water chemistry and lighting, etc., so that healthy coralline is a good indication that an aquarium's ecosystem is in balance. Lastly, of course, the colour and variegation of coralline is the quintessential decoration of the marine world.
If there is already coralline in the aquarium, algal spores circulating in the water will rapidly colonise any suitable surface, but it can also be introduced on the imported rock, or it can be 'seeded', i.e. by transplanting fragments/particles which have been scraped off existing live rocks - or other surfaces in an aquarium. Coralline algae requires a good supply of calcium to create the plant's hard cell-wall structure; in most situations the rock itself is the source, but where there is a deficiency (because of the density or composition of the base material) calcium supplements can be added to maintain concentration at 420 - 480mg/litre. (Crustaceans, molluscs and live coral also require calcium, and - depending on their demand and the form in which any extra calcium is introduced - some buffering may be needed in tank top-up water to hold pH between 8.2 and 8.4).
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