Adjusting a protein skimmer’s operational level and air intake is not always straight forward. Most hobbyists use the riser tube to make major adjustments, but the air intake can also be used. In my experience, as more bubbles are injected, the water and bubbles travel further up the protein skimmer’s neck. However, as you cut back on the air intake, the water level does not rise as far. Regardless of how the skimmer’s level is adjusted, you might want to double check its performance a couple of hours into operation. Case in point, I cleaned my EuroReef protein skimmer a couple of days ago. Shortly before going to bed, I readjusted where the foam head was developing in the neck and then walked away. The next morning, the skimmer was full to the top with a lightly colored skimmate and the return pump for the aquarium was sucking air. I was prepared to deal with the low water level fortunately, but it was a hassle nonetheless.