Too Much Light Or Not Enough??

I'm revamping my lighting system. I have a 75 gallon reef setup that has been established for 3 years now. Currently, I'm running 2 VHO's and 2 NO for a total of 300 watts. They are situated about 6 inches above the water level. I'm using 2 aquasuns and 2 actinics. My coral isn't really thriving like they should and these bulbs are almost a year old.

I've got another aquarium hood built and currently mounting my new lighting system in it. It will have 2 MH 175 watt 10,000K bulbs supplemented by either two 48 inch VHO or two NO. They will be situated about 18 - 20 inches above the water this time with a 3/16 inch sheet of Lexan between the water and the bulbs. Will the two MH and two VHO's or NO's be too much? Or should I just drop the supplemental lights altogether and run only the MH's by themselves? Thanks for any advice!

Actually, I think the lights are a little closer. I'm at work right now and don't have the hood in front of me. I didn't want the water to splash on the MH bulbs; thats the purpose of the clear Lexan. And I din't want the bulbs close to the Lexan, afraid of the Lexan getting too hot.

No shield, just bare bulbs. I made my own light reflector backing made out of aluminum sheeting and aluminum 'L' channels for stiffness. I'm using mogul bases for the MH's and waterproof end caps for the VHO's.