In most cases, a pink or orange residue or stain on your tub or fixtures indicates that you have a lot of iron content in your water. You can purchase a testing kit locally or online that will allow you to determine the exact mineral content of your water. If you use well water, you will probably need a filtering device or water softener to remove the excess minerals from the water before they enter your pipes.
The longer hard water stains remain on your tub and fixtures, the harder they are to remove. If the stains are minimal, you may be able to remove them with simple scouring power. You should avoid using anything with chlorine bleach. The bleach will actually set the stains and make them worse. Moderate to stubborn stains may require trisodium phosphate, muriatic acid, or oxalic acid. If using these products, be sure to read the directions carefully and follow all safety precautions.