IMO you should throw the rock out at this point.
I'm not sure if it would be safe for a fish only tank but it won't be safe for a reef. Inverts such as your snails and hermits would also perish they are very sensitive to copper.
If you really want to save the rock I guess you could cook it, which involves drying out the rock and washing it over and over again. Someone who's actually done it can explain it to you better if this is something you wish to pursue.
|