At the end of every good air compressor is a good air stone or air diffuser. The air stone or diffuser performs the task of breaking up the air that is being added to the ATU into small bubbles. The small bubbles maximize the surface area so that the most dissolved oxygen (DO) as possible can diffuse into the water. This dissolved oxygen is what the aerobic bacteria need in order to reproduce and consume the compounds in the waste water. Below are a couple of examples of air diffusers.