Copper with Nickel is an Alloy, it does not Corrode. It is used For Condensers which works best when submerged 6 foot into the lake, or pond. Research this alloy, try and find a tube or something and compare it to ss, Can also check a Local heating and cooling repair shop for a Sample, Tell them its an condenser/evaporator normally submurged 6 foot under, salvage a piece.