Aquarium lighting for a reef aquarium is very important. It is second in importance only to seawater quality. The lighting system needs careful consideration if corals are to prosper.
In a fish only system the lighting is not particularly important. The fish need to see and also be seen, that’s all. Two fluorescent tubes¸ one white and one actinic blue are sufficient. Two tubes are required in order to create a ‘dawn and dusk’ cycle. Of course, the aquarist could use more tubes if desired.
For the reef aquarium there are options. The aquarist could choose metal halide lighting¸ which is the most popular at the moment. This popularity is likely to change because halides are expensive to run and give out a lot of heat which can affect the seawater. The light of the future is the LED array though at present these are expensive to buy. They do not put heat into the aquarium and are much cheaper to run. There are also fluorescent tubes which have been available to aquarists for many years, which don’t develop the heat of a metal halide and are again cheaper to run.
Fluorescent tubes have developed over the years – T12 tubes, then T8’s, and then T5’s which are the current type. All types are still available though it is the latter one that is of most interest to aquarists. The numbers 12, 8, and 5 refer to the diameter of the tube.
The development of fluorescent lighting has included spectrum. Aquarists can choose tubes of differing spectrum. For example, a marine white tube will give a spectrum of around 10000K (K=Kelvin which is a measure of colour temperature). White is an important and much used colour in the aquarium. Another is blue actinic which is used by perhaps the majority of reef aquarists.
The reason why colour output is so important is because in the sea colours disappear at various depths – red disappears quickly¸ blue penetrates deeply so the corals are used to certain colours and require them (this is a generality). Within the flesh of most corals kept on a captive reef are zooxanthellae which are single celled algae. These algae require light of the correct type to flourish. This in turn means the coral will be healthy.
T5 tubes could be used for any coral as they can be obtained with the correct colour output. However, there is one more consideration and that is intensity.
Metal halides are powerful and can ‘punch’ light to the bottom of deep aquariums. T5 lights do not have as much ‘punch’ and this is the area where particular care needs to be taken. The aquarist who has decided to use T5 lighting should be aware of this limitation.
If the aquarist wishes to keep hard corals (SPS) then the aquarium needs to be shallow, or at least it does if the hard corals are to cover the reef. A depth of around 12” is probably the limit, though even then the aquarist will have to watch that corals lower down are settled. Not all corals require as much light so those that are happy with less can obviously be placed lower. It is probable that most success will be obtained in the top 6″ or 9″ from the surface.
Most aquarists will not be happy with an aquarium of 12″ or less depth. Most are 18″, 24″ or even more. If the desire is to have an entire reef of hard corals (SPS) then T5 lighting will not do, though blue actinic lighting can still be used.
If the aquarist wants to have a mixed coral reef, that is some hard corals and also soft corals, then T5 lighting could be used. As above the hard corals that need a lot of light will need to be placed in the top 6″ or 9″ from the surface. The rest of the reef can house corals that will accept less light such as many soft corals. Even so, the lower areas will be the place for corals that can settle with low light levels, there is a fair choice. Some aquarists do not like an arrangement as described as it could appear too stratified and unnatural. In this case the choice is really soft corals and those hard corals that can survive without high light intensity, though they will probably still require to be in higher areas of the reef.
Soft corals are generally easier to place, though once again care is needed to ensure that they receive sufficient light.
When fitting T5 fluorescent tubes it is advisable to use reflectors and to fit as many as possible lengthwise. These tubes need electronic ballasts and types that can drive two tubes are available which makes for more convenience. The tubes should be equally divided between marine white and actinic blue. Lay them out white then blue then white etc so that there is a good and even spread of both. If the tubes total an odd number, make the additional one a white. In addition the tubes should be fitted as close to the water surface as is practical to ensure maximum light availability. Creating a ‘dawn and dusk’ cycle is easy, just wire the blues and whites separately and make use of two electric timers.
T5’s are the latest incarnation in fluorescent lighting. The aquarist who makes use of them will have a good choice of lighting tube lengths and colours, and will also know that they are less expensive to run than metal halides. A number of tubes as described when housed in a close fitting hood generate quite a lot of heat so the aquarist should be aware of any effect this may have on seawater temperature, though any problem is not as great as with metal halides.
Success can be achieved with T5 lighting as long as the restrictions, mainly to do with depth of aquarium are taken into account. It is also important to change the tubes every 6 months to a year, the latest being a year. This is to minimize light intensity reduction and spectrum shift.