Shower Glass Doors won't come clean?

I am getting some kind of water stain (looks white in color, as if it were soap) on my glass shower doors. I can’t get it clean. So far I have tried “The Works'” which I know to be a very powerful cleaner, scrunge pads, pure soap, battery powered shower cleaners, and elbow grease. Any ideas as to what is causing the doors to stay dingy looking (they look clean when wet) and how to actually get them really clean?