Where I live we have very hard water.  Because of this hard water I have battled trying to keep my bathtubs clean.  I might add it’s been a losing battle.  The mineral deposits and soap scum accumulate faster than I can scrub it off.  I tried all of the products and nothing worked.  Our bathtubs are very old so they look bad very quickly. 

I discovered recently that a plastic mesh scrubbie, like you use to wash dishes works perfectly to clean all the crusted deposits off.  And it takes minimal muscle power.  A little comet or baking soda, some water and some scrubbing and you have a nice shiny tub.

So, if you are having a hard time getting your tub clean, try a plastic dish cleaning scrubbie.  It works for me!