OK...I know this is probably super duper stupid...but I just got a skimmer in my sump for the first time tonight. I know people talk about skimming wet or dry...and based on pictures, I know what each way is supposed to look like...But how does one control whether they skim wet or dry? I'm guessing it is regulated by where you let the water rise to in the body of the skimmer...but I really have no clue. Any advice is greatly appreciated.