Will have a chat to an industiral chemist tomorrow.
Funny story, but 25 years ago, one of my projects was to construct a CO2 storage (6 tonnes thermos style storage, not cryo), with evaporation to provide generator and PF mill inerting.
Was all brazed copper pipe, and massive oxide layer in the joints.
Chem clean company came in to clean the pipes on the cheap (as the supply Company said, they don't clean the oxide out in hospitals !!!)
Small above ground pool of citric acid, with a fire pump providing circulation as a batch tank.
Bloke shoves his hand in and tastes it..yeah, that's around 2...he was saving on test strips.