You have a 75 gallon tank right? Well looking at the specs for that skimmer, and take them as you will, it's rated for 120 gallons for a HEAVY bioload, and 240gallons for a light bioload. Now if you take those ratings to heart, unless you feed like absolute crazy a nuts amount of fish it simply is too much skimmer for your tank.
See the thing with skimmers is they really need to be sized appropriately for a given system, they remove dissolved organics, they do NOT remove nitrates, the problem is if your dissolved organics are too low the skimmer won't pull them out if it's too large, they cling to bubbles and need to "climb" (they get pushed from below) their way up the neck into the skimmer cup now if you have too low of a level of dissolved organics and the skimmer neck is too large they simply won't be pushed up into cup quick enough before the water pushes them out and end up back in your tank... where they eventually break down and form (eventually) ... NITRATES! so your tank got rid of the dissolved organics instead of the skimmer and unfortunately it turned them into nitrates which again your skimmer does not deal with.
One thing you might try, since it's a DC pump on the skimmer (presumably it has a controller), is to lower the speed on the pump to allow the stuff in the skimmer to persist more in the bubble chamber maybe then it can climb out. Other than that, I would say smaller skimmer necessary, but I can't recommend one since I have no idea what your bioload is like.