Hi. Yes, cerium oxide will do the job. The old-time glaziers/artisans still use jeweler's rouge. It's an awful lot of work to return it to clear and it's likely around the entire perimeter of the tank. The rule-of-thumb was always "if you can feel the scratch with your fingernail, it's too deep to bother."
Stop by a local glass and mirror shop. They'll have what you'll need and be able to explain the steps.
