I finally figured out exactly how to clean mold and any scum in my shower stall without the use of toxic products like bleach. My shower is tiled in natural stone and does a great job of resisting mold, but in summer, mold manages to get into the grout and rough areas of stone tile. All it takes to clean walls is a spray bottle, white vinegar, water, tea tree oil, lavender oil and a scrub brush.
Fill almost half with white vinegar
Few drops of tea tree and lavender oils
Spray mixture onto shower walls and allow to sit for a good ten minutes. Take a hand-held scrub brush and an old toothbrush for tight corners and scrub away. You may need to hit walls with shower spray if mixture dried. Hose off and voila! A clean shower with no harmful chemicals.
If the smell doesn't bother you, you can re-spray and allow mix dry to prevent future mold.
One other tip: I use a squeegee at the end of a shower and wipe down shower door and floor of stall to dry it faster--mold loves to grown in damp conditions, and this inhibits it.
For more recipes on cleaning and much more, go to: Harmonious Environment.