This external CO2 reactor using the patented impeller together with ceramic tube will ensure CO2 fully dissolve in the water, stay longer in the tank and increase the diffusion rate. It is small, save space but will ensure the best diffusing effect. The transparent chamber make visible to check water flow and speed of CO2 diffusion through internal impeller. The ceramic inside is easy to clean and replace. Suitable to use with external filter and canister filter.