The tank after I removed the driftwood and substrate:
Yeah, it's pretty nasty.
Here it is after I attacked the front pane with white vinegar and a lemon:
Lemons are beasts when it comes to hard water marks. I use them to clean water marks in my bathrooms every week. I'm not sure how well this will work out in the end, but if I can get most of the haze off the glass, I'll be happy.
I also don't know if my filter still works. It ran dry for a while (my kids hit the power button on the powerstrip and turned it on), so I'll have to mess with it. Hopefully it will still work...