I have an XP3 which I doesn't have the intake suction I had expected before purchasing. I can sometimes see minute particles floating right past its basket without even so much as a dip in the direction of the intake. All the media is clean and new, the pump is primed and operating, and water is being returned to the tank, but I've noticed an accumulation of waste all about the bottom of the tank. I previously had a sand and river rock substrate, so I think just never noticed the filter's usefulness, but I recently went substrateless, and I've noticed the issue.
I think my problem is that my stand height only puts the bottom of the intake about 8 inches from the top of canister itself, while the manual states 24" inches minimum. I did read some posts in this thread which seemed to imply height is not an issue, but as someone else said these types of filters essentially work on gravity and that height is an issue, i thought I'd post my situation here, and perhaps gain some guidance.