Red Sea Prism. Not a great skimmer but adequate when adjusted properly. IMO
these are a pain in the neck. I have one on my puffer tank (55) and it seems to constantly require adjustment. It often loses it's siphon.
Make sure you have good pump output and you haven't lost the siphon. Restore the siphon by opeining the flow valve & pinching the air tube until water has filled the inlet tube completly and you have full flow coming out the return. Let go of the air line (alowing air to be reintroduced to the pump inlet) and adjust the flow valve so the foam in the "reaction" chamber is just below the point where it enters the top chamber. If the skimmate is too watery you have the flow valve too far open. If you're not getting any skimmate, open the valve SLIGHTLY. A little at a time until you are seeing foam in the collection chamber. Give it a day between adjustments. It will require tweaking in this manner constantly. As the skimmer gets coated in bio-slime it works differently.
This is a good starter skimmer and will do the job with some care and maintenance. When you are tired of all the "care and maintenance", step up to a true venturi skimmer. A large one that uses a beefy pump. I am using a Red Sea Berlin Classic on my 75 with a Mag 7 pump. It does the job. All skimmer require cleaning now and again. The venturi gets plugged, the pump gets slimed up, blah, blah. The bigger and better the skimmer though, the less trouble.