There is supose to be air in there (usually the top 1") but you should still have effluent.
Check the efffluent tubing to the tank and see if it clogged (this happens on the intake as well). Try blowing out the tubing, and if the air does not pass through, what I do is use a long piece of aircraft wire of the correct diameter and snake the tubing (you could also replace the tubing). You should see the stuff that comes out!
It could also be pressure due to aragonite breakdown as noted below. Let us know what you find and if it is not fixed post a pic for us.
WF
__________________
I'm out. 
|