The acid idea sounds like a great way to save the rock. The tank silicone may still have some Cu in it but it could be pulled out with some absorber maybe.
So.... Acid bath for the rocks sounds like a cheap $$ idea. Just ensure to think everything through twice. Don't end up with a ruined floor or sidewalk! Or even a burned hand!
Then down the road you could try a test with an invert or two in the tank?
P.S. Really sorry to hear about this! I wouldn't even know where to begin if my tank crashed
