paint remover. The one i use was to remove the paints on my motorcycle. IT really stings a lot if you get it in contact with your skin. i dont know about water base and other solutions (see google images).
this is a glass tank? I have never had an issue removing paint from my tanks - if anything, it's getting it to adhere that is the problem. I would stay away form any chemicals - a sharp razor blade and elbow grease are your best bets. I did my 72" 150 in about 20 minutes.