Skimmer House Call

[Blue Ram]

So it must be a RS as it only runs on 1 pump. There is an airline control valve on the airline however I have never cleaned it. I guess I will start there. How do you know if it is wide open (I understand this is preferred) or closed? Second question is what does the water level adjuster do? On this skimmer it can be adjusted by rotating the pipe between open and closed however there is nothing to indicate which way you are turning it. The manual says to adjust it initially to "open" which is that the "open" sticker is facing or parallel to the skimmer body. When I had the entire skimmer out of the sump cleaning it over the weekend when I rotated the water level adjuster I couldn't see what was changing?? Is the water level in the sump critical to the skimmer?
Every time I feed the fish, I turn off the skimmer and recirculating pump so the food does not end up in the overflow. I have an auto topoff system on the tank. I have to adjust the skimmer every time I turn the pumps back on. Could I leave the skimmer running even with increased volume of water in the sump?
As I indicated, it would be much easier for me to have it explained in person while the skimmer is running.