Couple of notes to consider when designing your new one.
Your installed plexi looks to be good, but I would watch for warpage over time. I think you use the attachment hardware close enough that you won't have a problem though. I personally opted for a glass, sliding top.
On my 75 gal
, I have 6 T8 bulbs in my similar DIY canopy. All are ran ODNO 2X (which means the normal 32W bulb is running at about 48W). I opted for high gloss white paint for reflection (I actually WANTED to lose some light, to keep me closer to 3 or 3.5 WPG
). I have no fans installed, but I did only enclose about 1/2 of the back (only enclosed 15" on each side). I installed a black mesh type material to diffuse some light (works good too!). Anyway, before lighting, my tank temp is about 77F. After 10 hrs of light a day, tank temp rises to 79F. So, at least in my setup, the fans aren't as critical. I will probably be installed one or two on a 9V adapter in the near future, just for a little bit of help.