Lighting a Coral Reef Tank
Proper lighting in a reef tank is one of the most important determinants of whether the tank succeeds or fails. If there is too much light, algae will take over the tank and throw it out of balance. Too little light will make the coral pale and suffer. There are many different light systems advertised in the market today, including both fluorescent and incandescent. Spending time upfront before you add your corals to your tank will save you great expense and grief down the road.
Many corals use the “farming” method of eating. They grow algae in their tissues to harvest as food. This is a symbiotic relationship. The algae provide the coral food and oxygen and the coral provides the algae food from its wastes. These algae thrive and multiply through the process of photosynthesis- they harvest energy from light and turn it into chemical energy which the algae can use to expel oxygen. Photosynthesis requires adequate light and reef tanks that contain these “farmer coral” need to adjust the lighting so there is enough for the symbiotic algae but not enough to allow an algae bloom to get out of control and choke the tank.
The symbiotic algae contain pigments called chlorophyll “A” and “C”, which take in blue and red light for photosynthesis. Many reef aquarium lights will appear purple because they are a combination of red and blue lights.
The intensity of lighting is important as the wrong intensity can inhibit and eventually kill the symbiotic algae. The minimum light required is called the compensation point. This is the point where the oxygen that gets produced by photosynthesis is equal to oxygen requirements of the algae. Any less and the algae cannot effectively feed from the coral’s waste products. At the other end of the spectrum is the saturation point- the point where any further increase in light does not help speed up photosynthesis. Lighting in a reef tank must be maintained between these two points to keep the algae and the coral healthy.
The least expensive lights for the reef aquarist are regular 48 inches long fluorescent lights. Generally, six of these will be required- four “daylight” tubes and 2 Actinic tubes that produce blue light. They will have to be changed out every six months or so. Even though they will still seem to be bright to your eyes, the intensity drops over time. If you leave the lights in too long, you may notice damage to your corals. Compact fluorescent lights (CFL’s) are recent additions on the aquarium supplies market. They take up less space and give more output. You may consider these for a smaller tank space. In any case, the lights should be no more than four inches above the surface of the water. There are many reasons to not use standard incandescent lamps. The most important one is that they do not produce light in the correct spectrum for the algae. They also produce substantial heat which can heat the tank to dangerous levels. The final reason not to use them is the cost. Incandescents need to be replaced more frequently than fluorescents and cost far more over the life of the bulbs.
Lighting your reef aquarium is not difficult but it can be one of the more expensive parts of your aquarium and does take some time and planning upfront to keep your coral and fish happy and healthy.
