I've got the same
skimmer. It works nicely... although I wish the collection cup was bigger.
According to the people who make them, you want to keep it in about 6 to 10 inches of water for optimal performance. I don't really pay much attention to that... right now mine is prolly in a foot of water in my
sump and its working just fine.
PSH is right about the saltwater thing. Freshwater doesn't bubble up in the
skimmer like saltwater will, so if you want to test it out, test it with salt water (or you could try adding vinnegar... and then your house will smell like vinnegar for a day).
So... to set it up, you stick the powerhead on it (which I'm guessing you figured out), and pull the postfilter tube (where the water ends up coming out of the
skimmer) all the way down. The postfilter tube lets you adjust how much water is actually in the
skimmer body. The higher up you put the tube, the more water. You want to start it as low as it can go, and even then you might have your collection cup filling with clear water for a few days. Just let it run and overflow the collection cup until the water settles down if that happens.
Basically thats it... it's not too complicated. Water and air go into it, make an awsome little bubble storm, and the collection cup smells like fish poop after a few days.