What kind of skimmer is it? I run all mine with the water level just below the collection cup. There is a certain degree of trial and error with any skimmer in getting the best performance. Have you cleaned the throat on it lately? Sometimes it can clog up with gunk and greatly reduce performance. Also, for a day or two after you clean it, you may not see a lot of skimate being produced. You might be able to go to the manufacturers website and download a copy of the instruction manual...some companies offer them in PDF format.
Life is not measured by the number of breaths we take, but by the moments that take our breath away.