Getting Started in Reefkeeping, Part 3

Lighting

Unlike maintaining good water quality, lighting is one of the most controversial aspects of keeping a reef tank. In the early years of the hobby, tanks were simply lit with the single low wattage fluorescent tube that came with the hood. No thought was really given to using more light, as at that time the concept of keeping live corals and other inverts was not a consideration. Then in the mid 1980s, information - and even more convincing, pictures - began to arrive from Europe which demonstrated success in the maintenance of many marine invertebrates. One of the first things that stood out was the much stronger lighting that was used on these tanks. This improved lighting was the result of the aquarist's understanding of the relationship between light and the coral having algae within their tissue. This symbiotic relationship is due to nutrients being at low levels in the ocean. As a result, the corals have evolved to utilize the only energy source that is readily available: sunlight. By having zooanxthellae within their tissues corals are able to convert their waste products into usable products due to their relationship with the zooanxthellae. That is, during respiration corals give off carbon dioxide and ammonia that is absorbed by the zooanxthellae. The zooanxthellae then utilize these compounds during photosynthesis and produce oxygen and carbohydrates as by-products, which the coral then consumes. For this reason it is crucial that proper lighting be provided for corals in a reef tank.

The amount of light striking a reef can almost never be replicated in the home aquarium. This light has been measured to be between 110,000 and 120,000 lux at the surface of the reef and 20,000-25,000 lux one meter below the surface. While it may seem that all that would needed to be done would be to add more bulbs to reach these values, space and heat limitations make this impossible. Fortunately, the adaptability of many corals has allowed them to be kept successfully in closed systems where light levels may be as much as an order of magnitude less than they are on the reef.

The desire to match intensities found on the reef has led to a school of thought that light intensity is the critical factor for keeping corals. However, it has also been demonstrated that red and orange light is quickly absorbed by seawater and that blue light passes through seawater best. For this reason, the idea that spectrum is more important has developed a following. In the early days of reef keeping, two groups evolved: one that utilizes metal halide lamps and another which prefers fluorescent lamps. This dichotomy resulted because in the early days of the hobby only fluorescent lamps provided blue colored lamps, and only metal halide lamps could provide strong intensity. To further complicate the matters, in the early 1990s small polyped stony corals began to be maintained in many reef tanks. The general consensus was that since these corals typically came from clear shallow water only metal halide lighting could be used to keep them alive.

Fortunately, today there are a wide variety of options available when it comes to lighting a reef tank. Having all of these options available may make it just as difficult to make a choice as it was in the past. First, it is my opinion that an attempt should be made to light a reef tank as strongly as possible relative to the space available and what is affordable. To put it into general terms, the goal is to get at least 4-5 watts/gallon of balanced light above a reef tank. The choice of which type of lighting to use is a function of the tank's size, what is going to be kept and which type of light appeals to the owner. That is, for large tanks it is more cost effective to use metal halide lamps, while in smaller tanks it is more cost effective to use either very high output (VHO), power compact (PC) or the new T5 fluorescent lamps. However, even when getting down to choosing among the types of lighting, there are still more choices to be made. Therefore when choosing which type of lighting will be best and most appealing for your tank it may be a good idea to view similar sized tanks housing similar fish and corals to get an idea of what you like and what works. Even though looking at watts per gallon of light may provide a framework for how much light you need there is now even some question as to how valid this number is with the continued improvement in the efficiency of the lights available. Therefore this is one area where asking for help is usually a good idea.

Pictures related to this articles series can be found at here.

Mike Paletta is the author of The New Marine Aquarium and Ultimate Marine Aquariums. He has been in the hobby for over 15 years and has written numerous articles for Aquarium Fish Magazine, Tropical Fish Hobbyist and Aquarium Frontiers.