As it was explained to me. DE HQI bulbs are in a enclosed fixture for reasons other 'n to keep harmful UV wave lengths contained and filterd through the glass lens ( though that is one of the reasons.) It is because it must reach a certain operating temperature to achieve the correct color temp...
I've got a AGA 5.5 with three 32w PC bulbs. It has SPS and Clams. The light is not the problem,the heat is. I've got a Ice Probe in a AC mini to combat the temps and it works great.
No tricks. But because it's so small all the things get amplified. Make sure the temp is stable and evaporation is kept in check. I did make a little canopy and have two 7ws and a moonlight in mine. I also have a surface skimmer I made for the filter. I used a under the tank heater made for land...