Well here's the basic design I'm suggesting:
http://www.deltecusa.us/proteinskimmers/ap600.php
Note your skimmer is taller, I could be wrong - but the reaction chamber should be 5" on the AP600. So theoretically should be able to skim as well or better than the deltec.
Reason I said use the n/w pump in recirc is by having it feeding the skimmer, what happens is by the time your bubbles hit the reaction chamber, many have merged, and you've lost the microbubbles that are the whole reason for getting a needlewheel to begin with. By having it feeding directly to the reaction chamber you get finer bubbles for more efficient skimming. By reducing the flowthrough you're allowing longer contact time - more efficient skimming.
Andy