+1 for venting holes and/or a small "muffin" fan. One way or another too much heat is building up under that very closed hood.
You could also try leaving the feeding port open to see if that helps or use it to place the muffin fan over. If you elect to use the fan I would have it pull air out, not push air in.
Plan B might be to lose the hood entirely and buy another light. You will then have an open top tank of course.