Intense Precision Atomic+ CO2 Diffuser (With Built-in Check Valve)Precision Atomic+ CO2 Diffuser (With Built in Check Valve) Key Features: Super fine CO2 bubbles less than 0. 1mm diameter and highest diffusion rate. CO2 is capable of 100% dissolution in the aquarium water. Atomic+ series features high quality fixed suction cups and a built in check valve, to permit flow in one direction only. Standard 6mm CO2 tubing. Made by Intense, a well known brand for reliable, most efficient and built to last CO2 products.