I'll repeat that white vinegar and CLR are the best things to use. However, I have also diluted a small amount of Calgon water softener (usually used as a laundry additive) and had decent results with scrubbing stains around sinks and bathtubs.
For buildup around shower heads and faucets, take a plastic bag filled with the white vinegar, and rubber band it so that the buildup is soaking in the vinegar. Leave it overnight, and then take a rough sponge and scrub the remainder away in the morning. Usually, the buildup just sloughs off when you take the bag off, but I like to scrub it anyway for two reasons. 1) So the remainder doesn't dry up and you have to do it again because you have stains still, and 2) if you turn on the water while the buildup is still wet on the shower head it comes down on you. It doesn't hurt or anything, but it's slimy and gross.
Vinegar also helps with the dishes. You can use it while you're hand washing before you do your final rinse of each item, or you can put a cap-full in the dishwasher and it helps to minimize the stains on your "stainless" steel and/or glassware.
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