New rental house, rust spots and how to permanently get rid of Serratia marcescens

Moved into this house earlier this year and all seemed fine till the summer hit. Getting that pink bacteria and ive bleached down this tub 3 times now and about 3-4 weeks later it starts to come back!! Idk what to do or if its even possible to fully remove this. Ive replaced shower curtains the bath mat, fully bleached the tub 3 times and just cant seem to get it

Also looking for a way to remove rust spots from shaving cream cans on a fiberglass tub and granite countertops. Thanks!