For a short while I did the same thing on my thirty and had the same problem. I just took two blocks of wood and set them at the ends of the fixture, to raise it up about an inch. You can try and do that. Additionally, I'd recommend some daylight balanced bulbs. Home Depot sells some 6500k bulbs (daylight) for $7.96 They are 19w (i think) I'm currrently using one as part of a photosynthesis experiment with my 7th graders. Looks a lot better than the warm (aka yellow) bulbs that are mostly available.