Air stones are made of high quality non-toxic mineral material. With high temperature sintering, the stones are sturdy and durable, have high dissolved oxygen rate and create even and tiny bubbles rather than a limited number of large ones. Made of high quality and harmless mineral material Create tiny bubbles rather than bigger ones Keep providing oxygen for your fish to breathe Come with 2 PCS 4 inches air stone disc Disc shapes can stay steady at the bottom of your tank, while globe ones can produce more bubbles in the same size. You need an air pump more than 4 W to run this stone. Soak the stone completely in water about 1 hour before use. Clean regularly by a brush as they get clogged after weeks or months of usage. Replace the stone after it stops working properly.