question about my new skimmer

[Jarrett]

i have my new SWC bmk 150 protein skimmer running now i have the water intake knob closed fully and my question is about my fine adjustment knob (air intake) my bubbles medium size right now how does adjusting my fine adjustment work theirs a plus and minus. one obv makes the bubbles bigger and the other smaller what size bubbles should i be aiming for when i am skimming?

 

[Jarrett]

i also noticed when i play with the fine adjustment the water rises and falls depending on which way i turn the knob why is that