How do you get rid of rust in bath tub
Have you tried CLR-calcium, lime, rust? Ir is available at many stores including some larger grocery chains.
Bar Keepers Friend.
Here's a post that might help you - https://www.merrymaids.com/cleaning-tips/diy/remove-rust-stains-from-bathtub/
Cleaning pumice stone. I used in toilets , bathtubs and bathroom sinks. ( I used to clean apartments where college kids lived). I got mine from local wal-mart in the cleaning section. Did not scratch surface , that was my experience with it. I only used on porcelain though- not fiberglass.
Try WD-40. Spray it on and leave for a while and then wipe it off. It will dissolve rust but it will not stop it from coming back. It will need to re-surfaced to do that.