While shopping yesterday I purchased some river rocks. The packaging stated they were for aquarium, fountain, crafts, or candle accents. The labels stated one is tiger’s eye river rock and the other assorted river stones and river pebbles. Are they safe to add to my aquarium? If so, what prep should I do before adding them? I know to rinse them of dust and such but are other steps needed? I love the look of these but do not want to cause any harm to my tank.