Tools & Technique :
To prevent bathtub rings and soap-scum build-up, give your bathtub a quick wipe down with a soft cloth or sponge after every use.
Weekly cleaning with a mild detergent will keep your bathtub surfaces quite clean. If your bathtub has build-up of scale or soap-scum use a nylon brush or scrub pad with a multi purpose detergent. Never use abrasive cleaners or steel wool, especially on fiberglass or acrylic tubs.
Specialized Tools & Chemicals :
A good rust remover should be able to remove discoloration without scrubbing. Check the label to be sure it can be used on your particular bathtub surface.