I wouldn’t think of using vinegar in an aluminum pot. Acids can leach the aluminum out and I would expect MORE discoloration, not less.
I use a mixture of 1:1 distilled water and tap water to fill the canner. Distilled water will pit even stainless if used by itself, so mixing it with tap water cuts the hardness of the tap water so there’s less deposit from the hard water minerals.
Yes, there is some discoloration in the bottom of the canner up to the water line, but the metal does not look pitted or corroded. I put in a couple inches BEFORE I put the jars in to make sure its enough. By the time the jars are in the water level is sometimes about 1/3 the way up the jars, but it doesn’t matter because once the canner is up to pressure, the temperature of everything is up to the 240 F mark.
“Distilled water will pit even stainless if used by itself...”
The bottom of my C-Pap humidifier chamber is stainless steal and they said to only use distilled water. Which I have done for a long time and no pitting.