[ZLogic]

Would this achieve 2-3 watts per gallon with decent depth penetration for a 24" tall 40gal hex?

http://www.marinedepot.com/lighting_metal_halide_coralife_aqualight_advanced-ap.html

 

[Kathyy]

I use 3-150 watt MH across a 24" deep 96" long tank and coverage is fine and tank is bright on the substrate even though the tank is covered with scratched up acrylic and a layer of window screen. You probably would be fine with a 70 watt fixture.