Tunze 9002 - still not skimming..

[Nano]

heres a video showing what its doing.. er.. rather not doing
you can see the bubbles not even reaching to the bottom of the cup (which is a bit dirty on the inside, but the neck is clean)
usually after cleaning the skimmer, its working or at least starting to within a few hours. so again, the neck of the skimmer is clean, the cup is dirty on the inside though. I doubt that would be the cause. I have opened up the air a bit more since filming this, so we'll see if it helps.