Even though you constantly use your bath tub, rinse it with water and likewise, it does get dirty. You may not see real dirt, but the dimness on the surface can occur. This is mostly because of the minerals in the water, soap residuals, other. Here is some professional advice for cleaning these stains.
You can clean the bathtub without any professional help, with the items that are in your home, the cleaners Yiewsley say you need just a few items :
The last two are suggested for the cheapest cleaning possible. They can be found around any household, and both are great detergents.
You pour some vinegar onto the sponge and scrub everywhere you see a stain. This may not remove all of them though. Try making a paste from a little bit of water and baking soda. Make it just thick enough to sit on a surface of the tub. Cover the stains in it and leave for an hour to sit. Then rinse with water and work with the vinegar if you have not done so yet. Then rinse the whole surface with water, and wipe dry with a rag.
This will remove everything from mineral residuals, to the soapy ones.
Cleaners Yiewsley actually say that drying up the bath after taking one is a good thing. This will prevent the buildup to form and make the cleaning easier. Simply rinse the bathtub after you are finished and wipe dry with a cloth.
This is it, overall. No need for professional cleaning or anything. The harsher solutions for cleaning than the two we introduced can damage the covering of the bathtub, as well as a rough sponge can. So avoid them to the best you can.