Do I need a check valve for my CO2 system?
Check valves are used to prevent water from flowing out of the aquarium and pouring all over the regulator when it is turned off. The bubble counter in the Aquarium Co-Op regulator comes with a built-in check valve, but you can install a second one as backup if desired. We have personally used the regular plastic check valves with CO2 systems at our fish store, warehouse, and homes, and they have not broken down. That being said, CO2 does degrade plastic after a very long time, so we also offer a stainless steel version for greater durability.
For more information on CO2 systems in high tech planted tanks, read the full article.