Reef octopus nwb 110 skimmer problem

I hope someone here has had the same issue. My reef octopus nwb 110 doesn't seem to be working like others got there's to. I have tried raising it to 6" water depth and to about 7 1/2 inches nothing really helps. It does not seem to pull the dark skimmate out. I have had it on my 72g tank for about 3 months now tried adjusting it to super low to super high nothing seems to work the way it should. My love stock is a kole tang, mated pair of clowns and a purple firefish. And i feed well everyday. Any help would be appreciated! Need advice! Thanks!