Dirty and discolored looking fiberglass tub

You could try Bar Keepers Friend. The power type works the best. Sprinkle it on, add a bit of water just to dampen it. Use a sponge and very light pressure in case it does scratch. I have used it on my fiber glass shower and never had it scratch but I always start with light pressure when scrubbing.

Start with a paste of baking soda.

Agree barkeepers friend works great!

How to Clean a Fiberglass Bathtub

by Don Vandervort, HomeTips © 1997-2017

April 7, 2016

Fiberglass bathtubs are easy to maintain, but you must be careful with them because they are vulnerable to scratches. When you clean a fiberglass bathtub, take the following tips into consideration.

Never use abrasive cleaners of any type on a fiberglass surface. Scouring powders, steel wool, or other abrasive scouring pads and scrapers must be avoided.

Depending upon the cleaning needed, try these cleaning options. Make sure to apply all cleaners gently with a non-abrasive applicator such as a sponge, cloth, or brush made of nylon, polyethylene, or polyester.

• Liquid dishwashing soap or liquid laundry detergent.

• All-purpose household cleaners, such as liquid 409 or similar liquid bathroom cleaner

• Mild to moderate alkali solutions such as mixtures of baking soda with warm water, or a diluted TSP (trisodium phosphate) substitute in warm water (make sure it’s fully dissolved)

• Spic & Span® cleaning solution dissolved in a solution of 1 tablespoon per gallon

Always rinse the cleaned surface thoroughly to make sure no cleaning residue remains.

For stubborn areas, such as bathtub rings, you can make a paste out of baking soda and a little water. Wet down the tub’s surface and gently rub the paste onto it with a sponge, soft nylon brush, or cloth. Spray with white vinegar to foam up the baking soda, and gently scrub the areas with a sponge, nylon brush or cloth (anything soft so as not to scratch the tub). Rinse well with fresh water. (NOTE, this is my usual method of cleaning my bathtubs and showers.)

If that doesn't do it try Bar Keepers Friend, don't scrub too hard. Then if there is still grime in the bottom,get some Easy Off Fume Free Max oven cleaner.

i use iron out! Fill the tub with water and add a cup of iron out powder and leave overnight. When I drain the water the next day it looks new!

My tub is at least 20 years old and I have well water so it gets done every few weeks now that I have found a simple solution. Scrubbing never worked as well as the iron out does!