Marine tanks benefit a lot from surface skimming as that will improve the oxygen diffusion, not to mention removal of the oils that build up through feeding, coral slime, foam or even insects that land on the water surface.
I don't know how you are going to skim the surface without an overflow coz your water intake is similar to those reefers who use canisters without the benefit of a extra surface skimmer attachment.
I think the only way you can overcome such problems is to 'churn' the water surface with a powerhead such that it is never 'still'.