It helps to cultivate nitrifying bacteria and stabilizes the PH of fish tank. These are durable media that will last you for years and is small enough to fit in many hang-on-the-back filters. Just put it in a mesh bag and place it inside your filter. Creates lots of surface area for bacteria A scientific mixture used to purify water and resist algae growth. It also relieves fish pressure and the smell of fish tanks. Applicable to freshwater and marine environment. Manufacturing Date is on the product. Expiry Date is 2 years from the manufacturing date.