Eheim 2178 Professional 3e - Output and filter issue

[sciencefiction]

In essence would the pre-filter not block the same as the canister filter and thus cause the same issue if not more so by already reducing flow by the canister filter trying to drawer water through the pre-filter, at least ones such as the Eheim unit?

I don't get any reduction in filter flow by using a pre-filter sponge. I wash them once weekly or bi-weekly. I don't open the filters that much otherwise but all mine are full of coarse sponges as media, no floss. I also have a layer of some ceramic media too in each. It keeps the water pretty clean this way and does not restrict the flow. As Darrel said, pulling of the prefilter sponges to wash them will release gunk into the tank. I suppose the "jug method" helps 🙂 I just siphon it out once it settles at the bottom as I normally do a water change at the same time.

The reduction in flow in yours must be some sort of fault or design issue. I am not sure a pre-filter sponge will help much. The filter floss on the picture is not looking dirty enough to restrict flow but it seems there's a dent in it and as already suggested, it must be pulled in by the pump somehow, although I can't understand why would this be happening in the first instance if following the normal filter set up instructions.

For pre-filter sponges I use blocks of coarse enough foam. I just cut a hole in the middle(not all the way down) and slide the intake into it. Here's a picture of one of mine. The light in the tank is off, so not the best one I could take...It's not the most aesthetic solution and not for everyone's taste but it works great, and small fish love munching on these, so do shrimp.