Surface Agitaion Via Overflow Box & Sump?

[ikon]

would an overflow box alone prevent "skin" from growing on top of the water? also would the bubbles created by the drain in the sump create a sufficient o2 -> co2 exchange for the main tank?

 

[SkiFletch]

In your case with one pump feeding two overflows, probably not enough surface agitation to prevent surface scum. You're better off just having a powerhead pointed high and at the surface. As for oxygenation, yeah that coupled with your skimmer will create plenty of O2 for the water