I'm building a canopy here in the next few months for a 175w metal halide in a lumenarc mini reflector. About how high off the water should the bulb be to give me good enough spread to not create a spot light effect on the tank? I will be supplementing with my slimline s-12's in the time being until I can get a less bulky way to add some blue into my tank. I'm thinking of building the canopy 8-10'' tall. Any suggestions?