Hey Fitchguy. Welcome to 3reef!!!
What are the dimensions of your tank? This will help in laying out the lights.
Kelvin temps of the halides are more of a matter of taste. IMO you can have 2 different manufacturer's bulbs with the same Kelvin rating look totally different to your eyes  . I know that makes things a bit more complicated but for the most part a 10000K bulb is supposed to be a crisp white light and a 20,000K bulb is much bluer to the eyes. If you know the name brand of the bulb I can probably refer you to a couple of web pages that have color comparison pic's between the bulbs. I personally would generalize the kelvin rating and pick the bulb based on light intensity (PAR or PPFD) and the type of corals I am planning to keep in the aquarium.
Generally speaking you would use one metal halide for every two feet of length and two feet of width. Then the wattage or PAR values of the bulbs would be based on the depth of the tank and the type of coral you want to keep.
Enjoy,
Jim
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90 Gallon glass, 135#'s of rock and 2" sand. 2-250w 20k XM metal halides. 2-95 watt actinic VHO, 4 powerheads, Coralife skimmer. Maroon Gold Striped Clown, Blue Chromis, Kole Tang, Pygmy Angel, Serpent Star, Brittle Star,Gorgonians, Mushrooms, Yellow Polyps, Turbo Snails & Blue Legged Hermits. 20 gal sump with Caulerpa, Mag 7 return pump.
Last edited by Diver_1298; 11-13-2006 at 02:11 PM.
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Lighting in a 72" Canopy 4Xhalides 
