Right out of the box, they skim pretty dry. I ran mine with a bit less air than normal and it started to pull stuff out after a few days. The less air rises the water a bit, but not much. They are very sensitive to hands in the water. Mine wouldn't work for a few hours after my hand was in the tank.
If you want to improve it a little, try a better airvalve (I used one off from a penguin power head) and shorten the tube in the collection cup by and inch or so. Just those two changes make a large difference.
Google "seaclone mods" for other tips