By simply placing contents of Dog Rocks packet into your pets water bowl and filling it with no more than 2 liters of water your lawn will start to look greener and fresher. Dog Rocks hold special properties that help your loving pet fertilize your lawn not destroy it. Dog Rocks have been laboratory tested and are safe for your pets. Dog Rocks filter out impurities from water such as Tin ammonia and nitrates. These impurities are usually passed out through urine and when your grass comes in contact with these elements it is burned resulting in a dead yellow patch on your lawn. Without the impurities in the water Dog Rocks actually help your dog fertilize your lawn! This is great for you your dog and your lawn!. 200 Gram units work for 2 months.