How do I reduce the build up of calcification of hard water in bathtub after using the shower?

The tap water contains chlorine, calcium minerals. Is there a way to filter this stuff out of shower head so the water is free of minerals when I take a shower?

I spent several times a week cleaning the bathtub and bathroom tiles with comet. This stuff contains bleach powder that scrub the tub clean but it also cause scratches.

I am looking for an alternative liquid cleaner that doesn't scratch the tub but also clean the bathtub well like Mr. Clean