TOM TM1165 Aquarium Oxygen Stone 5-pcs. These oxygen stones oxygenates your aquarium when loss of electrical power occurs, or when transporting your fish. This small cylinder generates oxygen when immersed in water, enabling you to keep fish alive without the use of an air pump. Works by chemical reaction, oxygenating the water for 1 month. Not effervescent where bubbles are seen, but by a chemical reaction where 2 substances react together and create oxygen. Not reusable after opened. Suitable for both freshwater and marine. Active ingredients: Calcium Hydroxide and Calcium Peroxide. Recommended usage is one cylinder per 10 gallons with normal bio-load.