Does this tank have any top struts that connect the back panel to the front panel? If "no"...then these should be installed.
You can use lengths of 1" square acrylic rod from Tap Plastic to reinforce the back. This material is rigid and will counteract the bowing. Placement will depend somewhat upon the importance of esthetics. These components should be fused to the back panel with methylene chloride or other acrylic adhesive.
What brand is yours? Would you mind measuring exactly how much yours bows?
My tanks allready had a few repairs. Its no prom queen but I need it functional. Really diggin the wood "cage" idea. It could double as a cover for flaws as well.
Bottom line I guess is take what you can get and figure out how to use it. Monster tanks are very rare and very hard to come by around these parts...
I would make a nice wooden brace to frame the top and bottom all the way round and maybe some additional vertical bracing in the back. Would be worth a try. If it works just paint it black and it will look nice and be functional.
I second this option. I actually reccommended the same thing when you unveiled the tank in the photo lounge. A wooden top and bottom surround out of something like a 2x4. And then across the back some vertical 2x4's and a vertical part at each corner. The front corners would have to have a corner type brace putting pressure onthe front of the tank, pushing it into the frames. I would paint the back of the tank black first. And then you could make the frames look pretty good with some careful carpentry. Add some paint and i would have not problem sleeping with it or looking at it.
You could easily make a brace with 2 by 4s to slip over the top and maybe corner to solve your problem you could even paint or stain them to look nice.
the only thing I can think of is have a welder build you a frame for the whole tank to just drop in to- out of angle iron and straight iron for the top so it would slide in..or......have him weld on the top angle iron after you put the tank in the frame(if hes that good and wont melt the acrylic)