Like bang said,, start it slow then dial it up over a few days,,,,a good guide is the bottom of the 'bubble storm' should always be a few mm below the O-ring.
Now it's broken-in, mine runs best at 2/3 open,,, I empty the gunk out once or twice a month,,, it skims dark-green crap just like any other skimmer.
A lot of folk hate these skimmers but with patience they can be made to work just fine on smaller tanks (75g or less IMO).
Only complaint I've had after a year is the powerhead died and took a while to get a replacement.