The filter is a low flow, adds light aeration to the water and helps with the quality as far as keeping healthy balance of natural flora since I do frequent water changes. Also the substrate I use is almost neutrally buoyant and the light water movement allows water to flow through the substrate which prevents bad bacteria from colinsing in the bed.
As far as tank sizes go I think it is really works for you and the fish. If I felt like he wasn't a happy fish I would upgrade him in a second. Orville just loves playing in the different windows and I love watching him ; )