Ok, I see two significant issues.
1) Are those little cylinders actual biomedia, or are they course filtration? I got little rings like that that came with my eheim filter, and they were pretty smooth (low surface area) and designed to catch big chunks going into my filter so that they didn't block the finer filtration rather than serve as biomedia.
2) You might get better results if you do the same thing, except with the tube at the bottom and water coming out of the top. The way, the filter is driven by the pump and not simply by gravity (which may be an ineffective way to go about it. If you're getting good results with it the way it is, that's fine. If you try and scale it up though (such as getting a higher flow pump) you might run into issues.