You would probably have to "cure" it in freshwater. Usually when you buy live rock (I think you are reffering to live rock as "coral") you have to let it cure in saltwater without fish in it, because all of the organisms living in the pores of the rock will die and this can really mess with your water quality! This can take weeks or even months, and if you don't know how to do it, I would recommend looking through the saltwater forums for more info.