Scott Corbeil asked about the heat of Metal Halide lights. 1) the heat thrown by X watts of MH light is the same as the heat from X watts of FL lights. But you can easily have more watts of MH :) 2) 150 gallon tank wants 250+ watts of lighting. That's enough to warm the room in temperate climate and in hot weather, it means you wish for A/C or leave the windows open. Think of it as leaving the kitchen and bedroom lights on all day...