Naw.. Just watch out when acclimating corals to it.. some times they can "burn" if they're not adjusted to the bright light. Personally I've never seen this issue. Back when I had a 29g aquapod I had a 150w MH on it with no issues other than heat. A 20L will heat up pretty fast so watch the water temps under a MH.
Heat wont be an issue its in a cold basement. It will actually stop the heater from running constantly. the reason im considering my is I found a used one for a great price. I could have a 20l with fixture and nano koralias for under 180. Just didn't want to do it if I could "cook" them. Power consumption isnt a real big deal. To adjust them prob just put the light a little higher and adjust a shorter light cycle?
Cool thanks for all the input. Looks like I was on the right track. I was thinking of just making spacers to have the light sit higher while I start out the corals in the tank. Now I just need to figure out if I want to do sand or not. Never had a barebottom, but I'm sure would be nice to clean haha.