Is this mold, rust, or what?

Koo Kimberly 🌼 • ♡ •Intactivist •ProChoice •ProLGBT ♡
This has been in my apartment since I've moved here, and I can't get rid of it. I've tried bleach, cleaning vinegar, magic erasers, but nothing is working. 🙁 It's only in my bathtub/shower.