I dont know anything about the deltec, but a couple of points to note from my experience.
Where there is no/little bioload there is no waste for the skimmer to skim, so the bubbles will be very wet, or not at all
The stock skimmer air adjustment is extremely sensitive, literally the minutest of adjustments makes a lot of difference
Again with the stock skimmer it can take a while (a couple of hours) for the bubbles to build up to the skimmer cup, so I would start with it adjusted so that it doesnt reach the cup and leave it, but this may all be in vain if there is no bioload to skim - as per my 1st point
Good luck