Dog Rocks are made from a naturally occurring paramagnetic igneous rock found in Australia. When placed in your dog's water bowl these Rocks will remove 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 were directions are followed. However, if your dog has a pre-existing illness do not change their diet. Dog Rocks are only intended for use as stated. For the best results, replace your Dog Rocks every 2 months. Ensure your dog's water bowl is the main source of drinking water. Top up the water bowl each evening and replace water every few days. You should start to notice a change in your lawns appearance within 5 weeks. New patches should not appear! For dogs that play with the Rocks, place rocks into a water pitcher and fill water bowl from the pitcher. This is a 12 pack display case.