My BFF's mom has extremely hard water and a lot of iron in it as well. We got her tub/enclosure all clean, and then gave it a good dose of Marine paste wax. It helps to repel the iron and hard water scale. Makes cleaning with regular/more gentle bathroom cleaners easier too. We re wax it every couple of months, which is still easier than all of the scrubbing we used to have to do.
We did place one of the rubber mats in the bottom of the tub with suction cups on the bottom to keep her from slipping/falling :D:D:D