Was at the dollar store with my girlfriend and saw some black polished river rocks. This would make a very nice addition to my aquarium but they do not say anything about aquarium use on the bag. Ive done alittle research about picking out aquarium safe rocks and majority of the posts say to use vineger to drop on the rock and see if it will foam or fizz. I just dont want to assume since it says polished river rocks that there hasnt been anything added in them.