Basic theory of a skimmer is:
Protien sticks to the water surface.
Bubbles under water allow protien to grab on.
The more time the bubble remains in the water, the more protien gets stuck to the bubbles.
The taller the skimmer, the more time the bubble has to collect protien.
The more bubbles the better.
The protien stiffens the surface of the water, creating stiff, protien covered bubbles that the skimmer overflows into a collection dish.
So... get a skimmer that's as tall as possible for maximum reaction time, or get one that produces massive amounts of bubbles (air injected with water BEFORE going thru the pump)
This whole process was actually invented by Waste water engineers for use at your local sewage treatment site.