I have 3 Spider reflectors on my 6' tank. I originally bought 2 because of their claims but found that three worked better. I think they work well and help maximize the light output, but I don't think they work great when trying to span 3 feet.
I was looking for stuff to build my lights. In on of the 'ads' for the spider says you can get away with only 2 lights on a 6' tank. Since I have a 6' tank, this may be a way to save some money. The water depth in my tank will be only around 16". So, If these reflectors do what they say they do, I could get away with 2 250's instead of 3!
I have 2 250 watt MH with the spider reflectors on my 150. My tank depth before the DSB is 24". My tank is 5 feet long. I am about to add a 3rd halide so I can keep anything at any depth. At your depth, I would think it would depend on what you are going to keep. Keep in mind if you only put 2 MH you may want to add a 3rd later down the road. I like the spider reflectors, but I am not sure if they make a HUGE difference. HTH
