Marineland 100g in sump protein skimmer

[m1i1t1c1h1]

I recently got a 100g in sump protein skimmer from Marineland and installed it in a 20 gallon sump (for a 70g tank that is a year old). I am rather new to the whole salt water aquarium lifestyle and this is my first protein skimmer. I set the skimmer up last week and I am a little confused about how to make proper adjustments. At what water level (in the sump) do you get best results? And I am unsure about the water-air ratio in the tank as well. Whenever I add more water (by turning the knob no more than a millimeter) the bubbles get way too wet and the collection cup fills with clear water. Whenever I move it down (once again, by turning the knob no more than a millimeter) the bubbles don't even reach the top. Any advice for a newbie?

Thanks