Working principle very simple: keep the co2 in water long enough and mix it well with water until all dissolve.
Bubbles wanted to rise to the top, but get pushed down to the bottom by the water current from the pump.Bioballs break up the CO2 bubbles & let bubbles stick to the balls' surface for longer contact with water.
Water and dissolved CO2 exit from the bottom. Small pieces of filter fibre placed under the balls(not shown) to totally block any co2 bubbles from escaping.
CO2 100%溶解 if no bubbles escape to the surface, all disappear in the water.
I used glass ceramic diffuser b4 but find that many co2 escape to the water surface. I think maybe more than half the co2 escape and is very inefficient. But buying a co2 reactor costs > $100++ (just the reactor only, pump not included!). So diy. Look little ugly but it works. diy can't expect too much about look

. Hide it at corner, cover by plants look ok.