How to clean really dirty shower doors?

Glass shower doors
When I worked for a maid service while going through college, there were a lot of things that were a pain. There may have been nothing more daunting that glass shower doors though, as they just never seemed to come clean. We usually could clean a rather large sized how in under an hour, but if confronted with especially dirty shower doors we would end up being there a lot longer. Though many of them were hard to clean because of neglect or hard water, most of them would come out sparkling clean.
Can't leave anything on the door
We only had so many options when cleaning shower doors like that. We only had so many cleaning products, and we couldn’t use anything else unless specifically instructed to do so by the homeowner. Many times I would have to soak down the shower doors and go do something else for a while. When I came back some of the tough stuff would come off, but they would never be entirely cleaned to my liking. When cleaning a shower like this, you really can’t leave anything there. You also have to worry about the trim and the insides of the slide rail if there is one. You have to take care of the faucet as well.
Comet scrubbing
That’s when I would have to break out the Comet to clean the shower doors. I never liked to do it because my hands would be red and sore at the end of the day. However, I had to do my job, and if I had to get it out, I would do it. I would have to make a water and Comet paste to apply to the shower doors. In about ten minutes I could start the hard part. The scrubbing was brutal, but necessary.
Only the first time
Once the Comet has set the scrubbing was rather easy, but I would still have to scrub every inch of the shower doors to make sure they came clean. After that was over and they were wiped down, I would use a spritz of glass cleaner to make sure all of the Comet was off of the shower doors, and to give it a shine. Usually a shower only needed that type of treatment the first time we cleaned a house, but someone with hard water might need that every few months. If you are having problems with your doors, you may want to try the Comet.