Aqua Medic Membrane Diffuser 'Double' passive reactor w/ 2 membrane tubes for up to 50g. Direct 100% CO2 diffusion between membrane & water in opposing to conventional dispensing method. So, you see no ascending bubbles! Membrane allows only CO2 to pass through but not water, so it acts as a check valve too. It can take up to 40 bubbles / min. in high current area or 20 bubbles / min. in low current area. 4 vertical dispensing columns for food or medicinal tablets, etc. Imported from Germany. Aqua Medic Membrane Reactor (single). The Aqua Medic CO2 reactor does not dispense CO2 as a gas bubble into the water. It is rather diffused through the membrane tube directly into the water. The membrane tube consists of a special material which lets gas but no water through. This acts simultaneously as a check valve. The CO2 gas gets through the tube and dissolves on its surface directly in the water. Single reactor good for aquariums up to 50 gallons and may be used inside the aquarium or used externally.