CO2 reactor for filter outlet, tested almost 100% CO2 diffusion (since some bubbles may escape if you're not adding filter media or too much bubbles per second) but if you're using this for the filter outlet, you might as well add a wave maker to provide surface agitation since it will be occupying the filter outlet. Still a very effective design for its use and you can also add porous filter media for beneficial bacteria to live in and it will also help to diffuse the CO2.