Lighting the marine aquarium, wow, this could be a big subject! In fact it doesn’t need to be, as said on other occasions there isn’t a requirement to wear horn-rimmed glasses and a white coat when enjoying the marine aquarium hobby. Lighting has been written about before but seems to cause some confusion to newcomers so here are the foundations. There are basic requirements if success is to be achieved. The sun is the source of light for all life on earth and life is adapted to it. It follows then that in the aquarium the light must be suitable.
Let’s kick off with a fish only system. The fish need light in order for them to see and for the aquarist to see them. Fish also react to the presence of light or lack of it. When the sun goes down and darkness approaches the fish disappear into their hidey holes to rest and await the new day. When the dawn arrives and the light is strengthening fish will re-appear and begin looking for food. So light governs their life habits and it follows that this light cycle should be reasonably followed in the aquarium. It’s bad practice to plunge an aquarium into instant darkness or light. Intense light is not required for fish so using two timers, two lights, say tubes the length of the aquarium with reflectors, can be controlled so that at ‘dawn’ the first, blue, comes on then later, say 15 minutes or so, the second, white. When ‘dusk’ arrives the white light can go off and 15 minutes later the blue. The easiest suitable lighting is fluorescent tubes, one tube is ‘marine white’ and the other ‘marine blue’. A simple arrangement.
The reef aquarium also requires suitable light but in the presence of corals, soft or hard, things are a little more complicated and critical. The majority of corals require light as they have zooxanthellae within their flesh. Zooxanthellae are tiny single celled algae and there are really huge numbers of them in a coral. The algae/coral partnership is called symbiotic. The algae assist in the removal of waste products and in obtaining vital trace elements from the seawater. If this algae fails then the coral could turn white (generally called bleaching) and coral failure is very likely.
As with other plants the symbiotic algae require light to prosper. Corals have adapted to life at different levels of the reef and light colours disappear at different levels in the sea – red goes first with low penetration and blue penetrates the furthest. Some corals close to the surface receive the full spectrum, others lower down less. It has been found that if two types of light are provided then the corals are able to live and prosper, or perhaps rather the algae within them. Keeping things simple, the first light to use is ‘marine white’ and the second ‘marine blue’ as mentioned in the previous paragraph. The lights are not purely white and blue but we’re keeping things simple. Again the easiest lights to use are fluorescent tubes which are sold in the above white and blue. As many tubes as the aquarium will take lengthwise should be fitted remembering to use reflectors. If the number fitted is even they can be half white and half blue interspaced. If the number is odd, make the odd one white, again interspacing. Again they can be attached to two timers as in the previous paragraph, this will be good for the fish and the corals.
There is an occasion when fluorescent tubes won’t be suitable and that is with a deep aquarium. It is possible with such an aquarium to place corals closer to the top of the reef but this could tend to make it all look a bit unnatural. If the aquarium is deep, say 18″ (circa 46cm) to 24″ (circa 61cm) or more then different lighting could be considered. These depths should not be taken as ‘rules’ but as guidelines. Reef aquariums owned by some aquarists fluorish under fluorescent lights, the corals lower down being carefully selected. However, depth produces a definite light loss and it could be that more light power is required to assist penetration allowing easier and more general coral selection. Metal halide lights are often used, these usually hang above the aquarium and contain a bulb in each canopy. There is plenty of choice of bulb for the aquarist. The downside to metal halide is the running cost and heat generation. For example, two 250W (watt) bulbs obviously consume 500 watts per hour, half a kilowatt. Running costs need to be considered. It is best to use a blue fluorescent tube (or two if space requires it), so that the lighting can be ‘dawned’ and ‘dusked’ as mentioned earlier.
There is another and very good alternative to both metal halide and fluorescent tubes though purchase cost is a consideration. It is reasonably economic to run. This is LED lighting. It can be bought as a complete array that covers the whole of the surface area of the aquarium if the size equals a standard lighting unit size, or smaller arrays can be selected. LED lighting can also be bought in strips similar to fluorescent tubes. These can be placed over the aquarium in a similar way to fluorescents. The LED’s fitted are white and blue alternatively. They have the advantage that they do not emit excessive heat and also the bulbs last for many years. Fluorescent tubes and metal halide bulbs have to be regularly replaced even though to the human eye they appear to be fully functioning, replacement is usually after 9 months perhaps 12. Replacement is required because as the light unit ages the spectrum changes and intensity reduces.
Whether the aquarist is running a fish only or a reef aquarium lighting is important. It is second only, with coral lighting a close second, to seawater quality. High seawater quality and correct lighting should produce a beautiful aquarium and a definitely not frustrated aquarist.