Cleaning Ring Around Drain In Tub?

I just bought a house. It is a bit of a fixer upper but I absolutely love it. One thing though is this beautiful clawfoot bathtub. Sadly it has a ring around the drain part and is kinda stained a little yellowish around the bottom. I tried cleaning it, but I don't want to do too much to it b/c I don't want to damage the tub. Is it safe to use bleach to get rid of the yellow and how do I get rid of the ring? Please help =D Refinishing the tub isn't something I can do right now (and not sure I'd want to refinish this tub) so any suggestions other than that and replacing the tub are more than welcomed! Thanks! If I try the bleach and it doesn't work, how long should I wait until I try the limescale remover, so I avoid the toxic gas? (Thanks, I didn't know that!)