I've never owned a Deltec skimmer, so I really have no clue how to adjust it, but I did some checking around and found out 2 things about this skimmer.
One, it comes with a venturi tube. Do you have this hooked up and if yes, have you cleaned it lately?
Two, there is a plastic baffle atop the pump which can be altered? Have you tried that?
Live in the Western MD/West Virginia/DC Metro Area?
Join our very active regional forum Here
Like the advice someone just gave you? Add to their reputation! Click on the balance icon underneath their username and let them know.