I don't think he has a sump, I think it's a all in one nano and the skimmer sits in the back of the tank.trying to figure this out - is this skimmer in your sump? I should be in the first compartment and then there should be some kind of baffel for thewater to pass through - if you have the baffels and the return pump in the last chamber you should not be getting these bubbles going to the DT.
How about posting a pic of the skimmer "in action" and your sump etc so we can see if there may other problems lurking there