After reading OS's review
here I knew I had to get me one of these babies to tinker around with.
While it is a pretty good filter for the money, there are two basic design flaws. One of them, oversized O-rings, has been covered extensively, and is overcome easily, see link above.
The second becomes obvious when you look at how water flows through the filter media (a black and a white sponge in my case). The water enters on top, and is sucked out by the pump via a strainer that is sitting in the center of the canister housing. That means that only roughly the upper half of the filter media is actually being used. (Some slightly different models don't have the black bottom sponge and come with bioballs instead). This is exaggerated by the plastic strainer which is closed on the bottom and therefore prevents the pump from sucking water from the lower filter media.
This brings us to Modification #1.
is to redirect the pump inlet towards the bottom of the filter, so that water passes through all media before leaving the filter. This works, but a better approach might be the one described by Gunner here
and at the link mentioned above. By allowing the water to pass down between the surface of the sponge and the canister wall the surface of the media is greatly increased, which is a good thing.
Since I didn't feel like cutting up the whole sponge, I went a slightly different route.
On the bottom of the filter, I added some "Snap Over Rollers" that I had bought years ago in the $ Store just for that purpose. They will help to keep some space between the bottom of the filter and the lower sponge while not impeding flow.
Next, I made some cuts into both sponges, to allow some of the water to pass through to the bottom and being pulled through the lower black sponge.
Elastic sponges might close the newly cut channels over time, so I used some more of the handy Snap Rollers to prevent that from happening.
Finally, I cut off the bottom of the strainer which prevented water from the lower filter regions to be sucked in by the impeller. I put the strainer back to keep the white sponge in good shape.