A while ago I had a beer that after while started tasting funny, like a little bit too sweet. Not sure if it was bad or not. The keg I used with that beer, I noticed had two small reddish rust color spots in the very bottom. Not sure if they were two spots of rust or beer stone. I Cleaned the keg with my key cleaner using PBW, And then sanitized it. Looked in and those two little spots were still there. Then I soaked it in PBW overnight and still there. Most recently I put beer stone remover near 100% strength and layered the bottom of the keg with it for several hours and then put my arm down there with a scrubber and scrubbed and it’s still there. Left the beer stone remover in it overnight and those two spots are still there. Not sure if these spots are beer stone or two little spots of rust and if it could possibly be a source of ongoing infection.? Any ideas? I’m worried to put another beer in the keg now.