What filter, could be you're doing it right by not overfeeding or the pump isn't strong enough to circulate the debris to pick up.
You actually see the water moving through the filter since its a hang on tank type of filter. Is the water actually going through it and not over or around the filter pads and sponge? How have your water perameters been and how often do you do water changes. That filter is rated for up to 70 gallon tanks so you surface agitation should be fairly good.
Ok, you saw water where the sponge sits, but when it's running and you see the sponge, does the water go through the sponge or does it flow over or around it?
Do you even see water running out of the filter and causing water surface movement across the surface of the tank.
The spreader plate on top is distributing the water just fine over the filtering media underneath. Thing Im wondering about is the water actually running through the sponge pads since the filtering is gravity dependant. If you take a similar sponge and put it under a running tap, a lo of the water runs of to the sides. But if you put a clean floss cartridge under the tap, the water runs straight through. But you say all water perameters are fine and the few small parts of your glass, water, and water that I could see looked clean. All I would say at this point is that if it works, don't gix it.
