Since the tank was just being set up-transfer from a smaller tank-and no fish were in the 125, I used the rock to speed up the cycling. You always have to recure rock that has been shipped. They ship the rock somewhat dry, not submersed in water, with wet newspaper covering it. So some of the critters may die. If no fish are in the tank, just put it in. Be sure to run your skimmer. It will cure in no time.