I agree with Mat. A lot of people, when adding more LR to an established or cycled tank, usually cure it in a seperate tank so as to not disrupt the main tank. The spike, won't kill the rock, but the high levels of ammonia, nitrite or nitrate can cause harm to the tanks inhabitants. That's why most people don't add anything into their tanks until it has cycled or unless they are putting in some really hardy fish to help aid the cycling process...