I ordered the EdFred glass shower cleaner shown on Muchfun's link and tried it. It took a lot of elbow grease and I had to go over the shower door and wall a couple of times. Applied it with a Scotchbrite pad. I can't believe it actually worked. It was 10 years of hard water build-up. I tried everything imaginable to clean it and nothing worked. I even tried, over the years, using a razor blade to scrape it off and that didn't even work. I will be applying the Rain-X today and hope I can get DH to wipe down the door and wall after showering. Will also get some shower gel or use liquid soap. I sure hope that is the end of this very vexing problem.

Krissie is spot on. I posted this solution elsewhere. Bar Keepers Friend. I copied/pasted my original response below. I'd say good luck, but you won't need it... +++++++++++ I've tried everything over the years. Never had much luck with vinegar, fabric sheets, oven cleaner, and all the other suggestions. They kind of work, but not to my satisfaction. Plus, many are toxic. That's not how I'm going to go out. Then I happened upon a random posting online where a guy methodically tested all these different solutions in a controlled environment -- side by side in his shower. See URL below. Without a doubt, BARKEEPERS FRIEND is your solution. I've used it for several years since and it works wonders. My wife uses it to clean our kitchen sink and other surfaces. It's cheap and available everywhere. It doesn't scratch. Leaves no film. And isn't toxic like all those products that need "good ventilation." It's got oxilic acide or something like that. No scrubbing. Apply liquid or power (with water) with a sponge, do 3-4 circles, and wipe off. No sweat and instant gratification. A little car wax after cleaning and you're all set. Trust me. You can thank me later by verifying my suggestion... http://www.themanlyhousekeeper.com/2011/03/11/solved-soap-scum-and-hard-water-stains/ http://en.wikipedia.org/wiki/Bar_Keepers_Friend http://www.barkeepersfriend.com/

update - did all the checks from Bosch instructions and checked filters on all fixtures in the house. The two fixtures that had most dirty filter were kitchen sink and guest bath sink. The inlet water filter in the heater was a MESS - lots of clay dirt, tiny pieces of grass, and its physical condition is not good so it has to be replaced. We took it out and continue to use the heater as normal until we get replacement. It costs $7, and $7 shipping, so I am going to buy two - for the same cost of shipment - to make it worth the cost. Now that we have big filter in main line , this little one should not have too much work to do. I also changed a rubber washer in our showerhead to open water flow. I know these reducers are designed for city people to reduce their water bill, and we had it in the city, but now we dont need it. All this really opened up water flow and reduced problem but not completely. Right now temp setting is at 104, but the outlet hot water pipe temp reads at 115F. We should still do the multimeter check of the water temp sensors. But I was able to enjoy shower for the first time in longest time. Definately a noticeable improvement so thank you all! also, our PRV does not have a tap to check the pressure, so we will install a gauge in the line, and while we are at it - we will re-arrange the order of filter and PRV.

The tests you want are: 1. pH 2. TDS 3. iron (more on this below) 4. bacteria 5. sulfates 6. Nitrates 7. Hardness 8. Manganese 9. turbidity anything else that tends to be a problem in your area - a local lab will know what these items are. A little more about iron: When you run water from the tap, does it have noticeable color, odor or particulates? If so, you may have ferric (particulate) iron. Is the water clear as it comes from the tap? If you fill a glass and let it sit for a few hours, does it develop color or particulates? If so, you may have ferrous (clear-water, dissolved) iron. Look on your state's website and search for water labs. There should be a number of certified labs available. A local lab is your best option because they will know if there are any issues in your area that you need to be aware of, and the testing will happen more quickly which will vastly improve ferrous iron and volatiles (if applicable) accuracy.