By request here are some detailed photos of how I turned a so-so skimmer into one that is much quieter (no Venturi sucking air) and ultimately more efficient. Wooden air stones produce extremely fine bubbles so they are perfect for this application. Not to mention they are cheap to purchase or make your own (more on this later).
Really a simple matter of drilling a hole in the side of the skimmer, drill the hole so the airline you will be using fits very snug through the hole, it should take some effort to work it in there to keep is as watertight as possible. Feed enough airline through so that you can pull it through the top of the skimmer, add a limewood (or basswood) airstone and pull it back down. Leave yourself some working room on the feeding airline as the airstone will require routine replacement.
Don't mind the large air bubbles, that was me goofing around, an air pump will create super fine bubbles.
A note about placement of the stone itself, if you keep it a little over the skimmer's output you will get the maximum contact time for air/water, but more importantly this will give the micro bubbles a chance to rise before being drawn into the output and ultimately back into your sump/tank.
I recommend the TetraTrac Deep Water series air pumps, they will stand up to the high pressures of pushing air through wood. For this small skimmer I'm using a DW24-2 with both ports feeding into a gang valve to adjust the airflow. A decent needle valve will provide precise adjustments.
A quick overall shot.
This particular skimmer is on my 10g nano and is performing even better than I anticipated, with just a powerhead rated for 80gph. Got a bigger skimmer? Add two airstones.
Here she is in action on my 10g nano tank, right now running rather wet pulling sand sediment from the water column. Note the riser tube before the collection cup is about 4" tall... so she's generating a great head of foam.