Give it time. The bubles in the pic look fine. DOC
's will attach and move up the sides and over the top into the collection cup. It's probably still breaking in, or you don't have any DOC
's in your tank
If it was constantly producing skimmate you would have to emty the cup several times a day. Mine seems to just percolate until I turn the pump back on after a feeding, then it's producing skimmate for a day or so (I only feed every 2-3 days).