I use Dollar Tree Awesome Orange in the half gallon on my client's showers/tubs.
I clean professionally and I use a soap scum remover such as scrubbing bubbles or lysol power bath. Spray it on, let sit for several minutes and rinse. This is an alkali cleaner that breaks down the soap and mineral residue without damaging the surface.
This is the shower cleaner that we use to help keep grout and tiles clean and minimize the mildew - it works on kitchen grout too. Hope this helps! Hugs, Holly
PS - We have a FREE eBook with recipes for all of my homemade and all-natural cleaners. You can download it here --> https://pinkfortitude.com/thank#GreenClean