This is exactly the situation we ended up in. When the MH
were put into the canopy by the time you screwed the bulb in we were like 2" over the glass tops, if that (Oceanic tank/canopy). We're in the process of building a new canopy for it. We've purchased all the wood, we just need to get to work on it. We're going like 12" so that we'll have enough room.
There are some hamilton fixtures that are about 6.5 inches, as I recall. Check Captive Reefs.com. We have support beams inside our canopy so the fixture didn't fit in ours.
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