You need to either plumb in the overflow from your tank (as their less than ideal instructions indicate), or plumb in a powerhead or pump from inside your sump to provide water to the unit. You dont need an air pump. The pump that it comes with the skimmer (Rio 2100 or Oceanrunner 2700) then mixes the water and the air. I am using a maxi-jet 1200 to supply the water to mine, with the maxi-jet just sitting on the floor of my sump. Works great so far.
I plumbed in a small ball valve between the maxi-jet and the skimmer so that I can control the water flow. I used a combination of 1/2" cpvc pipe and vinyl tubing to make the connection.
The ideal water level is this: Take off the collection cup and watch the level in the skimmer body. It should be right at the top of the skimmer, but not overflowing. Place the collection cup back on and watch the wetness of the foam it produces over the next couple of hours. If the foam is too wet (liquid building up in the collection cup too fast) then cut back the water supply a bit.
The knobs don't do very much to control the foam quality. It is really the adjustment of the water supply. Also, skimmers do need a couple of weeks to break in to their best performance.
The foam will be hanging over the top of the collection cone, this is normal. The foam wil be an airy/ dry foam when it is working best, not thick and dense. The goo in the collection cup will be plenty gross from a nice, dry foam.
I hope that this helps. I was in the same boat as you about eight months ago. I have been in touch with Barry Torkington at Aqua Medic and he has helped me tremendously in getting my skimmer up and running smoothly. Feel free to ask me more questions if you want, I will try my best to help.
Good Luck,
-Christine
