To avoid rust formation, it is advisable to dry the tub thoroughly with a cloth after each use. If rust has already formed, treating the surface with baking soda or cream of tartar may be helpful.
For an even shinier result, continue the cleaning process with a vinegar and water solution. However, to remove limescale, vinegar is undoubtedly the ideal solution. Simply spray a cleaning mixture of water, vinegar and washing-up liquid into the bathtub and then pat the surface dry.
If you want to revitalize your bathtub instead, turpentine oil is the ideal natural solution.

Mix 20 grams of turpentine oil with a teaspoon of fine salt , apply evenly with a sponge, leave for a few minutes and rinse off the excess with water. After a few moments, the shine of the bathtub will be excellent without the use of harsh chemicals.
How often should the bathtub be cleaned?
In general, it is advisable to clean the bathroom weekly , paying particular attention to the sink and sanitary facilities. For the bathtub, monthly cleaning is usually sufficient, as it is frequently rinsed during use.