[Boatanchors] cleaning coppe, r and probably off topic but relevant to HF amplifiers.

[CLIVE COLLINS]

Good evening gentlemen,
Some time ago I read of a chemical that could be used in suspension to clean discoloration from copper PA tank coils. Unfortunately I have lost/mislaid the note that I made of the name of the chemical. Is there a chenist member who might be able to steer me to this chemical please?
Many thanks in advance.
Regards

Clive GW3WEQ North Wales Coast UK