Very possible... My parents old coral from before I was born. Been in storage for 20 or so years. Another thought, they used to treat it with bleach. Killed 2 of their tanks before they realized it was bad. Think they then started using a diluted bleach solution and that worked fine. Wondering if there was still alittle soaked in that my hot water rinse didn't get and it wasn't enough to harm the fish but it killed important bacteria in the tank.