If you are keeping photosynthetic corals (or clams), you will need enough light to meet their demands. This has absolutely nothing to do with water volume and it has very little to do with watts, which is simply a measurement of power consumption. Some 175w metal halide lamps (Ushio 175w 10,000K) produce three times as much PAR (photosynthetically active radiation) as other 175w metal halide lamps (Venture 175w 5500K), (Joshi & Morgan, May 2001). You would need three Ventures to equal one Ushio.
It is often difficult to adequately light small tanks to meet the needs of high-light demanding SPS corals because of overheating problems due to the small water volume. If you intend keeping SPS and/or any
Tridacna clams in your tank, I would suggest a minimum of a single 150w 10,000K HQI DE lamp -- either AB or Ice-Cap would be a good choice (Joshi & Marks, November 2002).
No matter what type of lighting you choose, the only important thing is the amount of useable radiation that strikes the surface of the animal. A PAR meter would be best for measuring this but a simple luxmeter will suffice. If the light incident on the surface of the animal is sufficient to exceed it's compensation point, photosynthesis will proceed. If it is not, it won't. You don't have to provide enough light to reach the saturation point, just enough to comfortably exceed the compensation point. The amount of light required to accomplish this varies greatly with different species of corals. You could keep a wide variety of soft corals with much less light than you would need for most SPS.
How much light you need for your situation depends on what you intend to keep and the efficiency of your lamps.
P.S. -- Here is something for you to think about
: A coral located exactly the same distance below a lamp receives exactly the same amount of radiation whether it is in a 20-gal tank or a 200-gal tank.
06-08-2004, 11:50 PM
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