If it's simply deposits from hard water, put a towel on the floor and lay the tank down on it with the offensive panel resting on the towel. Pour a 50/50 mix of vinegar and water inside the tank so that it covers the inside of the panel but doesn't spill over the plastic trim. Just let it sit for a few hours. Take a razor blade to it and see if there's a simple white residue left behind that comes off easily. Don't be surprised if there's still a little haze left after it dries. It may take more than one shot if it's bad enough. Be careful with the razor blade near the silicone beads. Hopefully you didn't use anything abrasive in trying to clean it up and scratched the glass.
If it fails completely, the glass may very well be etched....permanently, which is essentially fatal.
"Why can't my wife see all of this stuff as an investment?"