I've tried a passal of copper fouling cleaners. All of them used ammonia. Of those, Sweets did the best job of removing copper. That is until I tried KG-12. It's a water based copper solvent, doesn't smell bad and doesn't need neutralizing.
Tried an experiment using a copper penny. 1 drop of Sweet's on one penny and 1 drop of KG-12 on another. KG-12 was still dissolving copper when Sweet's quit.