i'm not familiar with the skimmer that you are using. any skimmer worth it's salt should be able to skim. our marine tanks are not as clean as can be seem by our naked eye.

fishes,corals and any living organisms found in your liverocks do produce a lot of waste. your skimmer shud be able to pull these out.

do experiment with your skimmer placement,paying attention to both the external and internal water level. not sure about your Weipro but some skimmers do better if the external water level do not fluctuate a lot.