Are you able to look into the body of the skimmer while it's running? If your tank is against the back of the wall, you'll most likely be unable to, but if you are, check to see how much water is spraying into the chamber, it should resemble what it would look like if you were to take a hose and spray into a bucket of water. Also, you can try my trick of elevating the exit side if the skimmer a bit like 1-2mm, this allows more bubbles to flow towards the reaction tower thus increasing output, hth.