To remove soap scum that is not too bad, hot water & a good scrub should do the trick. However, there are times we need to call on cleaning products to help us out. In this case, you simply need to use something acidic like Vinegar or Citric Acid.
WHAT YOU CAN USE
The one you find in the food isle next to the Balsamic & not the 'cleaning vinegar' which is not actually edible - because it is made from petroleum products! There is no need to dilute Vinegar for sprays or any solutions, it already has water in it.
one teaspoon of Citric Acid to one litre of water will make a solution with the same pH as Vinegar (around 2-2.5)
Watch out for porous surfaces like stone as it can stain & etch. Do a small test patch in inconspicuous area if safe go nuts!
HOW TO USE
Spray and Wipe
It is as simple as spray and wipe, using either Vinegar or Citric Acid solution in a spray bottle & spray the soap scummed surface.
Make a gel
Blend 1/2-1 teaspoons of Xanthan Gum to 500ml of Vinegar/Citric Acid Solution. This will thicken it up to a gel that is perfect for certain cleaning jobs.
WHAT'S THE SCIENCE?
It is all about pH. The pH scale measures if something is acidic (an acid) or alkali (a base or basic).
My nature most cleaning products are alkali or basic like laundry powders, dishwashing detergent, multipurpose sprays & SOAP SCUM. Then you have acidic cleaning products like fabric softeners, rinse aid, toilet & window cleaners. Do you notice anything there?
When you mix an acid with a base you are normally neutralising the effects. This is why you do not mix Vinegar with Bicarb unless you are doing a science experiment.