It all depends on what you want to achieve with it. With an O² diffuser you can enrich your tank with a lot of O² if you have massive problems with too little O², but you can also generate an excess of O² and thus an undersupply of CO², depending on your water values. A normal bubbling stone can also lead to the desired goal, while a diffuser overshoots the mark. I also recommend installing a diffuser on the water pump, which then sucks in O² above the water surface and mixes it with the outflowing H²O.