I'd try as Buzz suggested - put the rock into buckets with new saltwater. Let it sit a week, and test for copper. I'm afraid it will be permanently contaminated, though.
As for buying a used tank, asking the prior owner is the best way, but it isn't foolproof. If the tank was used as a reef, it's a safe bet, but if it was FW, all bets are off. Fill the tank, wait a few days and test for copper is the only think I know to do.
HTH,
Danielle
As for buying a used tank, asking the prior owner is the best way, but it isn't foolproof. If the tank was used as a reef, it's a safe bet, but if it was FW, all bets are off. Fill the tank, wait a few days and test for copper is the only think I know to do.
HTH,
Danielle