i have exactly that skimmer, heres the deal:
the amount of bubbles it makes is compleatly dependant on how far the pump is below the surface of the water. If you use the tube it comes with (its like 6 or 7 inches long) its practically impossible to balance the thing between not enough bubbles and too many bubbles.
Cut that black flexible vinyl tube that goes from the pump to the main chamber so its about 2 inches long... 1/2 inch of it is taken up from being pushed on the intake nozzle, and 1/2 inch taken up from being on the pump, giving you about 1 inch of space (where u can actually see bubbles flowing.)
Now, when you turn on the skimmer, have the dial valve shut to OFF, and the red flow knob set all the way low. At 1st its gonna make bubbles like crazy, so keep the red knob all the way down and only open the pump dial valve like... 1/2 way (enough to get bubbles up to about a centimeter into the clear reverse funnel tube.) You will (probably) see the main back big chamber thing totally full of bubbles. After a little while, for me sometimes around a few hours, sometimes over night, the thing calms down and the bottom half of the main chamber is clear (only bubbles above where they come out.)
At that point you can start opening up the grey dial valve until its all the way open. Once you get there, you can start opening the red valve up. It takes about a day in total to get it stabalized, but once it gets there it works really well.
Thing is, and I dont know about other skimmers, but you add any water to your system without shutting the grey dial valve all the way and the thing will f-r-e-a-k
out with the making bubbles, so dont forget when you top off or water change.
All in all, itll spit bubbles into the tank for a few hours but once it settles down, it wont spit bubbles into the tank anymore. (Eventually, the bubbles wont go below where they come out inside the main chamber... that unsidedown mushroom lookin plastic thing... and since the out tube is at the bottom of said chamber, no bubbles go into the fishtank)