Do you have the CLSC150SSS or the CLSC150INT?
If you have the CLSC150SSS, then your skimmer should be in 7.5"-8" of water.
If you have the CLSC150INT, then your skimmer should be in 6"-7" of water.
In terms of dialing the skimmer, here is a good read on how to: http://www.coralvue.com/support/317511-How-do-you-dial-in-a-protein-skimmer
Let me know if you have any other questions...