watts per gallon is a good benchmark untill you see a tank that completely blows it away. for example i run 130watts of pc light over my 20 gallon (6.7wpg) and keep acros, montis, clams, etc and everythign is doing fine and growing considerably. i met a reefer in denver who has a 600gallon tank, and runs 6 250 w hqi mh's and 8 32 watt pc actinics. if you take the time to figure this all out, it is running at about 2.3 wpg. This man has a green slimer acro that is as big as a basketball, and he has to prune it to keep it from growing out of the water (mind you it is now 6 years old as well) he has a table acro that is about as wide around as a large serving platter that is also 6 years old. which finally made me "see the Light" (sorry about the pun) that WPG doesnt matter, it is the intensity of the light that matters. he has football sized derasa and squamosa clams that chill on his sandbed, and two of the most beautiful plating colonies of Montipora Capricornis that i have ever seen (ive even got a frag of his orange one) Lighting is the most important part of a REEF tank. it is also one of the most higly debated topics on the board as well it should be. Just remember to not do what i did and get all set about watts per gallon cause then you meet guys like this who throw you right back to the drawing board and you have to, as Yoda so succintly put it "unlearn what you have learned"!
good luck
jon
