Key Features High Oxygen Air Cylinder Made of silica for the finest air bubbles For use within Aquariums Can also be used in ponds with the relevant airline. 9 Pack 65mm x 15mm High-oxygen air cylinders with protruding end caps to keep them clear of pond liners. Made of silica for finest air bubbles and long life. The 65 x 15mm air cylinder is designed for use within aquariums, but can be used in pond set ups with the relevent airline tubing and air pump set up. This is a Pack of 9