Dog Rocks are made from a natural paramagnetic igneous rock. When placed into your dog’s water bowl these rocks will remove any nitrates and tin found naturally in water. This will give your dog a cleaner, healthier source of water supply. Dog Rocks do NOT alter the pH urine balance in any way. Dog Rocks are not uniform size and differ from pack to pack in content because they are entirely natural. The weight of each pack is the same and therefore the efficiency consistent. There are no known harmful effects on dogs through the use of Dog Rocks where directions are followed. However, if your dog has a pre existing illness don’t change their diet. Dog Rocks are only intended for use as stated.