I would start with getting a K-2006 or similar that will show FC+CC both. I don't know what causes that sort of smell in a pool specifically, but I'd begin shocking it. At 80CYA you need to bring FC up to 20ppm and keep it there until you lose less than 1ppm FC from sundown to sunup (with the generator OFF). Don't use your salt generator to do the shock, use regular chlorox 6% plain (unscented) bleach or some liquid chlorine from a pool store if it's cheap enough. I wouldn't use dichlor or trichlor since you already have a CYA of 80.