the shower pan is a fiberglass/gel coated surface, right?
some cleaners may leave leave the gel coat MORE prone to future staining...
so look for one of the commercially available 'gel coat cleaners'...
megs's make one...
Oxidation Remover M4901 Product Information
but others are available too and might work, is there a boat supply store nearby?
as for preventing future stains, well....
that's the tricky issue, because WAXING the floor will leave it slick and hazardous for standing on.
my experience is the pink coloration gradually fades during showers and normal usage...
cheers
2air'