If it's acrylic - as I read in hints to Heloise, use a cheap shampoo. I use White Rain that is clear and $1 a bottle from Save-A-Lot. It cuts soap scum with little to no effort other than rubbing it on with a wet sponge. Rinse and the acrylic will shine. Works well on glass doors or sides too. Our shower is 13 years old and still looks like new. Don't know what the previous owner used though. We also have a sqeegy that we use after each shower.