Not sure what it would reactor class it would fall into, but it's basically the top half of a mountain dew bottle (I'm a junkie for the stuff) with a ~140 GPH pump mounted to the cap pushing water down into the bottle section. (The image is sideways, just realized. Sorry about that.) The airline is just in front of the output of the pump. The end of the bottle section has some floss media zip tied to it to minimize direct flow downward and to catch any bubbles that might be able to catch enough flow and be pushed out the bottom.
The theory is that the direct flow from the pump output, about 2cm across, pushes the bubbles coming out of the airline down, the bubbles can then escape the flow by moving radially outward, as the bottle becomes wider, and buoyancy will bring them back up to the output of the pump, where they start the trip all over again.
I've seen devices like this, but I can't remember what they were called or where I saw them. It seems to be much more efficient than the Hagen Ladder I was using, and is pretty interesting to watch with all the bubbles .