There are many ways to light a saltwater tank. From Mercury Vapor Spotlamps, to Metal Halodies, to VHO flourescents, to Power Compacts. Where does one begin? This article will deal with the typical aquarium. In other words, over 20 gallons, under 200 gallons, and not unusually deep (like a 55 gallon tank that is 24 inches deep, which we have seen). This does not take into account low light setups either, such as a nocturnal tank (lit by red light at night) filled with sun corals and cardinalfish, or a tank duplicating a cave, such as ones filled with gorgonians, sponges, and firefish. For understanding what the ratings on bulbs mean (like Wattages, bulb shape, etc.) see Dana Riddle’s article in "Marine Fish Monthly" July 1999.
The average saltwater aquarium needs at least 2 flourescent bulbs, the main brand in the States is Corallife. 1 bulb will just not make the average reef fish feel comfortable enough, as it may only be 10% of the light they would recieve in the wild, and mid-day would seem like evening to them. Two bulbs is best for a fish-only saltwater aquarium, one 10000K and one actnic blue seems to be a combination many people like, although it’s mainly personal preference with just fish. The higher the “K” the more blue "cooler" light the bulb produces.
There are a couple corals that could be tried with only 2 flourescent corallife bulbs. They must be placed near the very top of the tank though, and sometimes supplemented with foods such as newly hatched brine shrimp twice a month. For more information on why corals need light, we have devoted an article in the reefs section of this site on it. Also, an article on begginer corals that you may want to check out can be found as well. Zoanthids (Button polyps), Leather corals (except the Yellow Leather), Mushroom corals, and Green Star Polyps are some that can be tried. However, if you are going to seriously think about keeping corals, we always reccomeend the miniumn of at least 4 flourescents, with 6 being better.
With four flourescents, many soft corals can be kept. Even certain hard corals, if placed near the top of the aquarium, can be known to do fine. Bubble corals are a good example, along with Brain Corals. However, this is sometimes pushing it for long term care. For hard corals, we usually say 6 flourescent bulbs is minuimn. But if you are going with 6 regular flourescents, why not go with...
VHO bulbs! These are flourescent bulbs that are very high output. They give off much more light and are a great choice. 4 of these bulbs can make an incredible reef tank, and even certain SPS corals can be kept under them with success. Even the Giant Tridacna squamosa Clam can be tried. With higher types of lighting, a new ballast is usually needed. The Icecap ballast is exceptional, saving energy, and making the lights even brigher. Some people prefer VHO over even Metal Halodie, and they produce much less heat and are more energy efficient.
Mercury Vapor lights are mainly used for freshwater planted tanks, and while they are great for such, they are not used for reef tanks anymore really. They have never been overly popular in the United States.
Power Compact lighting is an exceptional choices. These are flourescents that are one ended. They are much better than VHO, and a great value. For large or small tanks, they excel, however, small reef tanks, say 30 gallons and under, they are most popularly used on. A great choice.
Almost all hermatypic corals (ones that take in light) do best under Metal Halodie lamps. Two of these bulbs may only amount to 30% of the light some shallow water corals have in the wild, so we are still needing to find a better source, which rumour has it will come in two years and blow everything else away.
M.H. bulbs produce lots of heat though, and are not as energy efficient as flourescents. Use a small computer fan in the hood to take out the heat. They also do not have as good a spectrum as flourescents, and must be placed at least 6 inches usually, and sometimes more, above the water surface. The amount of light obtained from them is uncomparable though, and they are ideal for reef tanks. Supplement them with two VHO actnic bulbs, and you will have the best lighting available; well worth the money.
Daylight is usually rated at 6500K. The 6500K bulbs are the best for M.H. The 5500K and 10000K are’nt bad though. For regular reef tanks, go with 6500K for sure. For tanks trying to duplicate deeper environments, 20000K may be in order. A higher K does not mean a better bulb, and many times it is a marketing technique because those bulbs cost alot more, and people therefore think they are better. It also depends on which depths your corals come from, as that is what they are used to. However, corals are highly adaptive animals.
Another great advanatage to M.H. is the fact that the light is not falling so evenly on the reef, which creates tons of shadows. The effects of having shadows of the fish and other animals, and the water rippling in particular, among the reef tank justify the higher price alone. It looks so much more natural and so much more alive you will never go back to floourescents.
This is to give you some comparisons on light sources for saltwater aquariums. Used systems and do-it-yourself hoods can save you hundreds of dollars. Good luck!