Skimmer Not Performing

[Palster]

I have been trying without success to control the algae problem in my tank for a while now (the tank has been running for about 6 months). I do not believe that my skimmer is producing near enough skimmate which could be contributing to the algae problem. I have a Red Sea Berlin skimmer (which I have read mixed reviews about). I am running a Rio 2100 pump with this skimmer. The pump puts out 692 gallons per hour according to the manufacturer. I have seen this same skimmer sold on-line with the Rio 2500 or 3100 pump which puts out 782 or 900 gallons per hour respectively. I have the air screw on this skimmer unscrewed all the way so that the venturi is receiving maximum air flow. Even with the air screw backed off all the way the skimmer will not produce a wet skimmate and the production seems to be poor (I am only getting about half a cup of skimmate per week). I am wondering if maybe the pump that I am using is undersized for this skimmer? The instruction manual that came with the skimmer states that the minimum pump size should be 500 gallons per hour so my pump is well above this.