This is a 4 ounce bottle of Hartz Aqua Aid-Acriflavine. It is used to help aid and control fish that may be coming down with ich, tailrot or fin. The nice thing about this product is you do not have to isolate your fish from the main tank, just add 1 tablespoon per 5 gallons of water to your tank. The main active ingrediants in Aqua Aid are acriflavine and methylene blue.