BobTheDog
Fish Fanatic
I would strongly advise boiling any rocks before adding to your tank. Even if the rocks appear to have been dry for quite some time many types of microorganisms can "encyst" themselves... basically going into a state of suspended animation. At some point in the future, when they become wet again, the cyst will dissolve and the organism will become active again. Some microorganisms also reproduce through a process which produces extremely hardy spores. These spores also become active in the presence of water. It is quite possible that you could go all your life adding untreated rocks to your aquariums and never have an ounce of trouble, but why take the risk?
