[Myka]

If there is an airline clog, EuroReefs will overflow, not stop skimming. Seems to me the skimmer is getting too much air. I am guessing when you clean it, you are removing a partial clog, and then the skimmer gets too much air, water line drops, and the bubbles don't reach the collection cup. Turn the knob to restrict air to the skimmer a bit, the water line should go up, and the bubbles should reach the collection cup. Once you have set the skimmer in its new "freshly cleaned" setting it should be good to go. When you notice the skimmer starting to skim wetter than usual you will need to clean the airline tubing or the venturi where the airline goes in. If you are on top of it, you will notice it getting wetter before it overflows.

Also, anytime you clean the collection cup, when you first plug the skimmer in use the airline to suck up some freshwater to clean the airline tubing. You will still eventually get a calcium deposit on the venturi where the airline goes in, but rinsing does help.

HTH.