Hagen Fluval 20g-co2 Diffuser. The Fluval CO2 20 Diffuser is ideal for use in planted nano aquariums, including Fluval's Flora Aquatic Plant Kit. The clear, acrylic diffuser allows accurate viewing of CO2 storage and provides hassle-free distribution. The diffuser is easy to disassemble for cleaning, and is also easy to put back together. The Fluval CO2 20 Diffuser can also be used with all pressurized CO2 systems for aquariums.