How do I get rid of yellowish staining in my tub?

http://homeguides.sfgate.com/remove-bathtub-discoloration-36779.html

A mixture of dawn dish soap, baking soda and lots of scrubbing

If it's not a colored bathtub (white only) you can try oven cleaner. It's got lye in it so wear gloves and protect your face. Also make sure you have good ventilation. Use your ceiling fan. And don't leave it on for more than ten minutes or so. Don't walk away or you might forget about it. Try a small spot in a not too visible area as a test run first. Good luck.

If it’s enamel finish use ammonia. Porcelain denture cleaner tabs ( Dollar Tree at least 5 on on a strip of them;) diluted to workable paste and apply and leave for awhile and see if that works. Trial & error;) Good luck!🌺

Try a rust remover product

If it's a white tub, I'd use bleach. Water it down a little and little and let it set a few minutes before scrubbing clean.

Thank you but I've already tried using bleach. It lightened it but is still showing.

I’ve just finished with a shower stall of white ceramic tile. I probably tried 8-10 products. FINALLY, I discovered ZAP ( make sure it is not Zep). ZAp is an amazing product. Follow the instructions and you will have a fresh white tub!

lime away

Id bleach it