I love my Black Tahoe but it hard-water spotted really bad one time and all the waxing, rubbing and whining I did wouldn't get rid of them! I tried to get a couple of the local body shops to buff the entire Tahoe out but they either don't have time or the cost was just crazy. Finally I went to see a friend of mine with a body shop and he gave a tip that I wanted to share here. He said they used to spend several hours "wheeling out" water spots. He showed me a bottle of Aluminum Brightner, It is an acid they use on semi truck tanks and wheels. The phosphoric acid type cleaner is less aggressive than sulfuric and hydrofluoric so watch what your buying and go with less aggressive. IMPORTANT: Dilute the solution (1 part acid to 5 parts water) in a spray bottle. Wash the vehicle. If you have plastic trim try to avoid spraying the solution on it. Only work on one panel at a time by wetting the panel with water and then spraying solution on panel. Rinse well before it dries! You may have to repeat a couple times but it works great and is much easier and cheaper then buffing the vehicle out and you wont have swirl marks. Give a good waxing and you'll be pleased with the results.