I agree with Jim - easy does it. Tell us about the rock. Was it lighted, heated, etc?

My aptasia grows just fine without light. Personally, if I had rock with all of THAT on/in it, I'd put it on the deck for a couple of weeks with fresh water on it. Then run it heated with saltwater for a couple of weeks, making sure the water parameters were fine, then I'd add it very slowly to the main tank, monitoring it. Pests are insanely difficult to get rid of once introduced.