I recently broke one by doing something stupid. Had it on the floor while doing some cleaning and knocked a glass jar off a table . . . landed just right to break part of the lid.
Probably best to get a piece of glass cut to replace the broken panel as long as the hinge is still in good condition. Is it 1/8" or 3/16" thick glass?
lowes has some cheap thin glass they'll cut for a few bucks. It's def not the sturdiest but would be a quick fix. I think it's about time you put up some pics of your 2 tanks