The Berlin skimmer is IMO (from my experiencing owning one mind you) one of the most inefficient skimmers out there. They use a venturi cone to create the foam and it just doesn't work very well.
The key to these skimmers is a pump that can cope with a huge amount of head pressure. I'm betting it was that Marine Depot Rio/Berlin combo that I got suckered into buying once. The Rio is not a suitable pump for this skimmer, get rid of it and use a Mag 9.5, or an equivelant Quiet one or Eheim pump. If you really want to fix it, you can also drive it with a pressure rated pump such as an Iwaki 40RLT.
I ended up replacing mine, but another approach I thought of was to buy a needle wheel type venturi pump or something like that, and remove the venturi cone all together from the Berlin. There are some very outstanding venturi pumps out there, particularly the new stuff that uses mesh wheels to shred the air.
