Lights above the water

i have mine about 10 inches or so from bulb to water and things seem to be doing well. I got a red cap growing on the floor of my tank. so i think the penetration is fine

 

Mine are about 12 in off the water and like snowman said i can grow sps on the bottom as well.

 

alot depends on the reflector cheap spider reflectors 8-10in good lumen bright reflectors 12-14 inches

 

what watts and what tank size?

 

i too have 20k 400w hamiltons and 2 VHO actinics on a cheap homemade reflector/hood. i dont loose much light due to height, i loose more of mine out the sides of the tank cause the reflector dont aim the light strait down in the tank like i'd like it to, but for now it does its job and will get modified someday

 

My MH are 12 inches from the water. Position and quality of the reflector will play an important role in light penetration. I have a canopy on the DT so I don't lose lighting on the ends...I have heard many people say they lose it from the ends. Those that do can use a taller (like bamboo) or hanging plant (ex: airplane) next to it and take advantage of that light