Green rust = copper?

[FitoPharmer]

I am taking care of a large tank. I found out on day 1 the ATO is just running straight off a copper line into the tank. I have turned off the ATO and have been manually adding RO/DI water until the new tunze ATO arrives. My question was, I noticed the metal arm of the float valve for the ATO has some green rust on it. Does that mean this piece is either made of copper or is a copper alloy?