Rippling the surface does nothing for gas exchange, there has to be a break in the water for proper gas exchange.
Correct me if I'm wrong but I was under the impression that surface agitation created by powerheads helps break up the film on top of the water for filter's to pick up.
Breaking this film in turn creates a larger surface area for gas exchange to occur.
__________________ Adam 90 gal reef, 30 gal sump, Tunze 9015 skimmer, 2 X Tunze Turbelle Stream 6125, Coralife Aqualight Pro 2x 250 w DE & 2x 96 w PC, 9 w Turbotwist UV sterilizer, 2LF phosban & GFO reactors