I don't know, I have had nothing but problems with rocks not purchased from a reputable pet store. With some rocks my water was always cloudy and the rocks seemed to be shedding small pieces. Even some of the rocks I purchased at a lfs had a tendency to mess around with my PH. I like what rich311k suggested. First boil the heck out of them (about an hour or more) to kill anything living on the rocks which can pose a problem to the tank. Do not clean them with any kind of soap or detergents - just boil the heck out of them. You might want to scrub the rocks with a medium grade brush under running water before boiling to aid the process. Then after the boiling place them in a large bucket or tank filled with dechlorinated water and monitor the water chemistry - Good luck and let me know how it worked out - Right now I boiling driftwood fro my tank.
