How do I remove bacteria, mildew, and soap s in a shower stall without having to scrub it all the time?

The pink bacteria *I believe it's called Seratia* is always growing on the walls of my fibergl shower stall. Black mildew is always growing in the groves of the metal frame to the shower door. Soap s or filmy residue is always on the gl shower door. I scrub it about every week or every other week, but this stuff keeps coming back. What can I do so that I don't have to scrub it so much... I don't want to buy anything very expensive... I saw those automatic shower cleaners but they are too much money for me... Does anyone have any ideas, or have had something that worked for you?