Elemental O2 Cylinder Stones accelerate oxygen replenishment and increase water circulation when used with a high-output air pump. The 2” O2 Cylinder Stone has a 2” diameter and is compatible with 3/16” ID tubing. These are large stones, and they put out a ton of air. It is important that you have a capable air pump, like one of our commercial pumps, in order to get the most out of these great air stones.