If you have the following skimmer:
http://www.coralvue.com/classic-160-protein-skimmer-570
Then the skimmer should be in 8-9.5" of water. No more than that.
To dial a skimmer, please refer to the following support article... http://www.coralvue.com/support/317511-How-do-you-dial-in-a-protein-skimmer