well you dont need to polish out the scratches completely, just rounding off the edges of the scratch will dramatically reduce its appearance. mind you if the glass is thick enough and you've got the time you might as well do a proper job.
just remember to use plenty of compound and the fastest speed on your drill with a regular water spritz from a greenhouse mister to keep it wet.
Canadian tire, Rona, home depot, home hardware. Used to use them at my old job. They will help reduce appearance but may not get rid of it entirely. If you can't get it all put adjust your tanks lighting to hide it.