Besides what the above post stated, when I put new rocks in my tank from the out side, I bake them at 400 for about an hour.
Why I bake them now is once I placed rocks in the boiling water and waited until they cooled and was ready to put them in my tank. I noticed snails came out of a rock crevice still alive. I did not think anything could survive boiling water but it did.
It creeped me out, so now I don't take chances.