do you have an overflow box? if so, the overflow removes any film floating on top of the water restricting oxygen exchange. if your tank is topless, even better. i don't think i have any added surface agitation(no powerheads facing upward or anything like that), and my tank is fine. i really think that overall current in the tank and the skimmer is enough. [/i]
OH REALLY! I had always assumed that the reason surface agitation added oxygen was becuase of the bubbles not becuase of film on the surface!
Learned something new today!
I don't have an overflow box... just a mechanical filter that had rising/falling water in it to change currents and add bacteria to a sponge. I took all that stuff out and have a steady current instead of falling/rising.
Took out all the floss/carbon week ago....just an empty filter for flow....
I think I'm just going to take it off completely and add a power head now....
If you do have surface agitation, do it without causing bubbles. I like to see currents flowing at the surface of my tank, but if bubbles of any size are forming and popping you will get lots of salt builup on lights, the edges of the tank, and really anything within about a foot of the tank. Get rid of the bubbles and you'll get rid of salt creep.
Even if you don't have an oily film on the surface of the water, the water does have a natural surface tension layer that will limit gas exchange somewhat. Although surface agitation is not necessary for gas exchange, it will help by breaking that surface tension layer.
Basically, circulation is always a good thing, so get as much of it as you can. A skimmer alone is probably fine to keep everything alive and most things healthy, but more is generally better in this case.