Juwel 125 Powerhead

Did you clean both the impeller and the impeller well? They can get covered with goo which slows the flow. Use a cotton bud to clean inside the impeller well but be careful the end doesn't come off or you'll need tweezers to get it out (I speak from experience  )
What about the white pad? That is first in the direction of flow to catch bits of debris and it gets clogged quickly. It doesn't wash well either. It will need changing often, and it is much cheaper to buy a length of filter wool/floss off a roll and cut it to shape.

Things to try before spending money on a new pump 

Most filters have filter wool as the last stage to 'polish' the water - that is, remove the fine bits that go straight through a sponge. Juwel decided to put filter wool as the first stage instead; they say this is to catch large particles to stop them getting into the sponges. This means it gets clogged a lot more quickly that the filter wool in the other makes.