The marine aquarium has two main types, the fish only (FO) and the reef. These systems have a good few things in common, one that is not common to them is the aquarium lighting.
Water quality is the number one requisite in a marine aquarium, and this is closely followed by the lighting (for a reef). The new aquarist can be forgiven for being confused over quite a few areas of marine equipment, and lighting can be one of these.
In the planning stage, the aquarist has decided what type of aquarium to keep. On many (most?) occasions this will be a reef. There are quite a few others who decide on a fish only. This may be because when listing the necessary equipment the cost proved to be too high, or simply that the aquarist intends to gain experience first and/or wants to keep fish that are unsuitable for a reef.
Anyway, the aquarist has made a choice for whatever reason. This makes the choice of lighting easier.
If the aquarium is going to be a FO, then there are only two reasons that lighting is provided – the first so that the fish can see and have a daylight/night cycle and the second so that the aquarist can see the fish. This means two fluorescent tubes that have a suitable colour spectrum for marine. The tubes could be T8’s or better T5’s. One could be daylight and the other actinic. The sole purpose of the ‘proper’ spectrum is to show the wonderful fish colours to full advantage.
The reef system needs more thought, and more money. The fish have the same requirements as those in the FO. The placing of corals in the aquarium is what causes pause for thought.
Many corals (but not all) have symbiotic algae (Zooxanthellae) which are necessary to the corals. This algae, like others, needs lighting of suitable power and spectrum. Failure to provide the correct lighting power, taking into account the depth of the aquarium, and spectrum can lead to problems with the corals. At least a bank of T5 fluorescent tubes running the length of the aquarium, and as many as will fit, taking into account reflectors, from front to back is required. A good mix is half marine daylight and half actinic. If the corals are the soft variety, this may well be sufficient. If they are the hard variety, they may be sufficient if the hard corals are placed in the top third of the reef.
If the aquarium is to be a hard coral reef and perhaps one or two soft types are to be kept lower down, the best current lighting type is metal halide. This lighting is a bulb or bulbs in a reflective canopy, the bulbs being 75 watts (w) up to 400w. It is possible to obtain bulbs which are even more powerful. The bulbs come in a variety of ‘spectrums’, annotated as Kelvin (k). The current vogue seems to be for 14000k, sometimes higher. The higher the number, the more blue, or cold, the light appears. Aquarists often supplement the metal halide lights with actinic fluorescent tubes, in an attempt to ensure that the symbiotic algae receive the correct lighting, and this helps give an attractive appearance to the aquarium.
There is one more check that needs to be made, and that is running costs. Metal halides are quite expensive to run, and along with heaters and/or coolers (chillers) the electricity bill could be substantial. It is worth checking the running cost before making a decision.
Lighting in itself is a complex scientific subject. However, the beginner needn’t worry about this, but just needs to make sure that the lighting chosen represents an acceptable onwards cost to run, and that it is suitable for the intended livestock. There is a great deal of non-technical information available.
Very basically, if running a FO aquarium the aquarist can choose fluorescent tubes. It is probably best to use T5’s, particularly if the aquarium is fairly deep. If running a soft coral reef, fluorescent tubes can be used, but more of them as above. If running a hard coral reef, metal halides (possibly with actinic fluorescent tubes) are better, particularly if the aquarium is fairly deep.