Have to agree, the bubbling you see as your water trickles into the tank is nothing. Spatter that water against an RBC, and you increase the water to air contact, and add O2. Also the constant rotation of the RBC itself, picking up a thin layer of water, exposing it to air, and re depositing it in the tank, does way more than that little bit of bubbling you see. People always think of aeration the wrong way. For instance, an air stone itself adds little O2 to the water, it is the constant upcurrent that it causes that adds O2. Water to air contact.
