It's not adjustable, but you can get a surface skimmer box for it. As fishfreek pointed out though, after buying one, you have to be very diligent about keeping the water level up so the skimmer doesn't run out of water. The Aqua C will pull a good bit out of the water without the skimmer box though. What size tank do you have? The Remora is good for up to about a 55 gal
...above that and you're better off with the Remora Pro and a Mag 3 to drive it. If you buy a Remora, get it with the MJ1200 powerhead instead of the Rio. Check the sponsor forum for places to buy one if you're interested.
One other thing you might do is up the flow in your tank...that will help keep the DOC
's from accumulating on the top so much. HTH