It is a reef octopus classic 90, I moved it to the other side of the tank yesterday so that i could remove the variable of the water level in the return chamber from the picture and it seems much more stable there. I do not have any pictures of it in that location but there is a picture of the skimmer a couple of posts back. In the new location it appeared to be skimming, it was not a constant rate but it would build up a bit then bubble up the neck and into the cup then back down the bubble level goes to just at the start of the neck and a while later it would biuld up and go. This skimmer is overkill for my tank, I have to fish in 20 gallons of tank.