skimmer problems

[ganowicki]

I have a 125g aquarium it has about 40lbs of LR, sand bed and 2 fish in it. it has been running for about 4 weeks. I have a Red Sea berlin turbo skimmer and I have noticed that it has not filled up the skimmer cup in the last 2 weeks. the the inside of the cup has a thick mud like sludge coating it, but it never fills with any liquid. I have tried to adjust the air intake to give it more of a wet foam instead of a dry foam, but it does not seem to work. could it be that my tank is too new to be able to skim very much or is it that the skimmer is really not that good or am I doing something wrong??