Time, and perhaps over-tightening, can lead to the tank glass becoming stuck. Here's a more reliable way to remove it without cutting yourself or destroying the glass.
First find something grippy like this non-slip, rubbery material
Next wrap it enough times round the glass to protect your fingers in case the glass is weak.
If needed hold the metal part steady with just enough grip from a vice. Wiggle and turn and with luck it'll happen. Warming or cooling might also be tried.
