if it was used in a reef tank and then left out i would def. cure the rock and not put it in your system do to all the leaching that will occur especially if you have corals such as sps.
i would throw it in a rubbermaid with rodi saltwater and a skimmer (cause im crazy like that :lol2 most people use regular rodi water and everything but the skimmer and keep changing water out every once in a while, heater and water movement such as a powerhead and let that rock leach out whatever it has. just the way i am i would also throw a phosban reactor with phosban. also please do yourself a favor and ask the owner of that rock if he used copper in that tank he had it in. if it was a reef i would hope not but you never no...