Hi Carl...
Yeah, this product 'tis a puzzlement. The front "Active Ingredients" list shows Cyanuric acid 96% and Inert Ingredients 4%.

Then, way over near the bottom on the back it lists the product's California registration number and below that is...Contains: Cyanuric acid, sulfuric acid, water. Each ingredient has a CAS# (whatever that is) associated with it, including a number for "water."

Container contents definitely sound dry to me when I shake it.