With idk whats on this rock if your really scared about putting in or not you could always bleach it then remove the bleach =o bleach should remove ANYTHING but it can be tricky to much and its hard to get back out of the rock @,@ and taking he bleach out can be done with other products most saltwater fish stores have i think o.o; gl ( i bleached some of mine to remove copper still using the same rock today with inverts/ect make sure to use a bucket you'll never use for anything else =o fill with water then add some bleach DON'T add a lot less is better then more.)