Using a skimmer to “remove the floating proteins” is not recommended in freshwater aquariums. The water movement at the surface needs to be slow for these to work. “Slow” water movement at the surface means poor aeration, which is very unhealthy for the fish. There is also no such thing as “floating protein” in a freshwater aquarium (floating bacteria, fats and oils, yes, floating protein no). And the skimmer is taking the most oxygenated water in the aquarium and sending it to the filter.
There was a video of a hobbyist who was using a skimmer in their aquarium. They were pointing the filter return down into the aquarium to keep the surface flow minimized for the surface skimmer. Now if they had a sump filter with a trickle filter they were fine, they had a good aeration point in their system.
If they had a submersed static media bed such as a canister filter they were in for a disaster. They had no place where they were doing aeration. Never combine a “calm water” skimmer with a canister filter or a submerged static media sump filter. An aquarium needs aeration if it has any significant number of fish in it.
Spray bars can be effective if the pump that creates the “spray” is powerful enough to create a true high-velocity jet of water. That water is aimed tangentially at the surface of the water one inch or so above the waterline of the aquarium. Unfortunately, many canister pumps don’t have a high enough pressure and the spray bar becomes a “dribble” bar. “Dribble” bars don’t aerate well.
Also, note that the pumps for most commercial aquarium filters are not high-pressure pumps. A spray bar resists flow. It creates a “head”. So the low-pressure pumps have real problems if coupled with spray bars. This head will significantly reduce the flow through all the standard filter setups that use spray bars. Most spray bars are also very noisy if they are placed above the water line of the aquarium.
If one finds a pump powerful enough to overcome the head of the spray bar, we recommend putting the spray bar below the waterline. Place the spray bar aimed up at 30 degrees or so to create a large area of “choppy waves” and good aeration.
Source: Aquariumscience.org – David Bogert