NOT Rain Dance that's car wax.... RAINX..... makes glass so slick nothing can stick to it.
And now
major secret revealed
Wait till the shower tiles are completely dry,
then buff them with 0000 steel wool.
It MUST be 0000 and no water of any kind.
What will happen is all the soap film ends up in the wool pads.
(I guess for our OZ and Inglesi friends, they should use the finest steel available whatever the rating.)
You can also use 0000 to take those water spots off the chrome and brass fittings. And buff all the spittle off the mirrors!!
What happens next is the tiles are so slick the hard water can't stick to them just rebuff with the 0000 every couple of weeks.
Joe