Normal airline tubing can lose up to 20% of CO2 through its membrane. Silicone tubing reacts with CO2 and renders it less efficient (causing the silicone hardening over time under CO2 usage.) This special CO2 resistant tubing loses less than 1% of CO2. Also perfect for saltwater use on calcium or kalkwasser reactors. 4/6mm ID/OD. Can be used regular air line tubing for air pumps and their accessories for kinking problem. This tubing will fit all 3/16" air stones and manifolds normally used for aquarium devices. Always use a non return check valve.