I don't currently surface skim my reefs mainly because:
1. Im not feeding heavily, and carry a relatively low dissolved organic compound mass considering the systems are unskimmed. In a system housing an anemone that may have been fed chunks of silversides or other meaty foods, the fats and oils emitted in digestion will weigh down a water column much faster than a standard small reef that does not house anemones.
2. I feel the DOC's that stay in the system due to the lack of skimming are great foods for corals of all kinds. The trick is not to carry such a heavy suspended organic load, just enough to provide slightly rich water for your lightly-fed corals.
3. Powerheads can be aimed and turbulence can be re-routed (especially with those link-lines) to stir up the surface, even a grossly underskimmed system will not carry a surface scum if agitation is strong.
Ehiem makes a fine over-the-back surface skimmer if any one of these variables will be compromised in your current nano reef. And, heavy skimming can remove many compounds before they accumulate at the water surface--if it doesnt work with a particular skimmer either upsize it or install two. Dissolved organic load sets the stage for algae wars, increased nitrate levels, and distribution of elements such as phosphorus and nitrogen throughout a system. But in the right balance it is also beneficial for corals, as they make use of these proteins and compounds when they are ingested in one way or another.
BrandonM.
