This decision is often taken in the planning stage, when considerations of equipment arise – what is needed? Some equipment is duplicated whatever the system type.
Beauty is in the eye of the beholder. This is true for marine systems. Many would say a mixed reef is the ideal, but all types have advantages, and some would say there are disadvantages too, mainly in [tag-self]aquarium maintenance[/tag-self].
This system is often set up nowadays not as a bare-bones fish tank but with live rock. Strangely enough it then becomes a ‘fish only with live rock’ (FOWLR) which seems pretty reasonable! The live rock is not essential, but it will assist with [tag-self]aquarium filtration[/tag-self] and provide a more natural décor. Perhaps herbivorous fish will find something to browse on, and maybe other life may appear. With or without live rock, the fish only system, size for size, will be the least expensive in hardware.
Equipment can be as basic as canister filters for bio-filtration and an efficient protein skimmer, plus heater(s) and circulation pump(s). Some aquarists go further and have a sump or refugium with a DSB and algae bed. The lighting needs to be two fluorescents as there is only a need to see the fish and for the fish to see. Some aquarists use a blue and a white with electric timers, so that each tube can be turned on and off in sequence (blue on first and off last).
The main advantages to the fish only system are that, first, the aquarist can consider a larger range of fish for the collection. They do not need to be reef compatible, only compatible with one another and their size relative to the aquarium. So some beautiful fish are available such as many butterfly and angel fishes. The fish bio-load can be higher, that is, there can be more fish for the aquarium net gallonage. The second advantage is that water quality need not be so high as in a coral system. For example, nitrates can climb a little higher. However, water quality is still important and efforts need to be made to keep it as good as possible. The fish do not have different water conditions to the corals on the wild reef!
Coral only systems usually use live rock which is formed into a reef, on which the corals are sited. As with the fish only system, there is a need for heaters and an efficient protein skimmer. However, the bio-load presented by corals is very much lower than that of fish, so it could be said that the skimmer is not as essential. However, a skimmer should be placed on the aquarium though it will not produce as much skimmate. Some corals are fed, but the potential load on the bio-filters is not usually as high as it is with fish. Additional equipment may be required, such as a calcium reactor, depending on the type of corals kept. There will be a need to keep a closer eye on water parameters, and more of them, than in a fish only system. Many aquarists with this type of system will have a sump with a DSB and perhaps an algae bed.
Lighting needs more consideration. It may be that the aquarist needs to use metal halide at the outset if the corals are SPS (hard corals) possibly supplemented by blue actinic fluorescent tubes. If the corals are the soft variety, fluorescent tubes are often sufficient. T5 tubes are often good for this, a mixture of marine whites and blues. There is no need for staggered light turn on and off unless the aquarist particularly desires it.
The advantage with the coral only aquarium is to do with water quality. The bio-load is low. There aren’t any fish with their natural life functions including the need to feed. The possibility of a nitrate or phosphate build up is much lower – with routine water changes it should be nearly non-existent. All things being equal, the corals should thrive.
This to many is the choice to make, as it represents the closest that an aquarist can come to a wild reef. A properly managed and healthy captive mixed reef is something to fully admire, because of the colours of the corals and the movement of the fish. So it would seem the one to choose. Well, many do, but there are considerations before the plunge is made.
The great advantage with the mixed reef is, as said, the picture it creates. Watching the fish swim among live rock covered in many corals is aquarist heaven. Lighting considerations are as in the corals only system, as the corals are the livestock that make the demand. An efficient protein skimmer is necessary, and bio-filters must be adequate. As with the coral only system, additional equipment may be required.
This type of system needs disciplined [tag-self]aquarium care[/tag-self]. Why? Because the fish are downgrading the water quality, with their normal life functions and with the need to feed. The corals need high water quality, and all the additional parameters that exist in a coral only system need to be maintained, despite the fish. A strict maintenance routine is required. It is generally normal with this type of system for a sump/refugium to be kept, with a DSB and perhaps an algae bed.
There is another disadvantage, one that does not occur in a coral only system and one that is more easily dealt with in a fish only system. If a fish becomes diseased, it is far more difficult to deal with in a mixed reef. In a fish only system a fish can be separated out more easily, or if necessary the whole aquarium dealt with (live rock if used can be a problem). For instance, say a fish shows evidence of marine ‘white spot’ or ’velvet’. In the fish only system the aquarist can use a copper based medication, which is known to be effective if used correctly. Copper is deadly to corals, so cannot be used in a mixed reef system. There are plant based and other treatments for diseases, but as far as I am aware they are not fully effective as can be copper. (I would be delighted to be advised that I am wrong, with the name of a reef safe treatment that does work.) Either the fish must be captured and removed using a capture device, a very difficult exercise in itself as it is likely to hide in the reef, or the reef must be dismantled at least partially to catch the fish. An aquarist may be lucky and be able to net the fish out, but this is unlikely. Even if the fish is successfully removed, fish diseases such as the two examples spread alarmingly quickly in the confines of an aquarium, so there is the danger that the disease remains in the aquarium. This leads to potential total fish stock loss, a sad state of affairs. It follows that fish additions to a mixed reef should go through a quarantine process.
So the three choices of aquarium system are all desirable, and all show advantages.
It is clear that the fish only system, properly stocked, is ’easiest’, but this is not a yardstick except for those who are fully beginners. Anyway, what a sight, such beautiful fish.
The coral only system places some more demands on the aquarist relating to lighting and water quality. Beautiful as this reef system can be, most aquarists will not be able to resist the addition of fishes over time.
So that is perhaps the best way. The aquarist who just must have corals starts off with a corals only system. Checking of water parameters and routine maintenance will bring experience keeping corals healthy and vibrant. When the system is stable, and all is well, small reef safe fish could be added slowly, a constant watch being kept on water quality, and allowing the bio-filtration to adapt. With just a few fish, the aquarist may well be satisfied. Keeping just a few small colourful reef safe fish adds the extra dimension required. Keeping the fish load low, less than the maximum guideline for a reef, is a compromise that helps protect the success of the reef through the water quality.