I guess that it is possible to get nasties in your rock,but I myself have never had a problem.I have added alot of rock from many diferent shops to my tank and have never quarenteened any of it.Also,have never had a problem. I think if we were to worry about every little thing that could possibly get into out tanks,it would take alot of the enjoyment out of it for me.If you start worrying about rock,What about the sand,Food,and pretty much anything that comes near the tank????Hope you see my point here.Enjoy your tank,and try not too worry too much.