I'm running a System 3 with a 46oz DIY apple juice bottle which has a biowheel. My method of injection is just a 1/4" elbow hose barb from home depot into the filter uptake. Bottle lasts 2+ weeks (I just change it every other water change) and I'm holding 40+/- ppm of CO2. I keep the return right at the water line for minimal surface disturbance. jtm