Acrylic material does not stain easily because of its non-porous quality; however, that does not mean surface stains won’t develop on acrylic bathtubs. Mold, mildew or even brown rust spots from metal objects left on the tub commonly cause surface stains. You can clean these off the tub, but you have to be careful what products you use, as acrylic surfaces can be damaged by abrasives or solvents.
Put on rubber gloves. Spray a commercial, non-abrasive bathtub cleaner on the stained areas and let it sit for 15 minutes, or the time indicated by the label on the bottle.
Dampen a soft sponge and scrub the stained areas. Light staining or fresh stains may be easily removed this way. If the stain is still there, don’t worry--there are other ways to remove the stain.
Rinse out the bathtub to remove the cleaner and dry it with a towel. Apply fibreglass/acrylic cleaner (a common brand name is Gel Gloss) on the stains with a soft dry cloth, as advised by the Mrs. Clean USA website, rubbing it briskly into the stained area.
Allow the product to dry on the bathtub. As it dries, it looks hazy--don’t be alarmed, that's how it is supposed to look.
Use another clean, dry cloth to buff off the haze. Beneath this, the stains should be gone and your tub should look polished and the area will be more stain-resistant. If you have time and energy now, you can use this on the entire bathtub.
Prevent future stains by cleaning the tub regularly and keeping objects off the surface of the tub--moisture gets trapped beneath razors, bottles and other items and leads to stains.