The skimmer is maxspect d600 water level 20cm and the tank is 170g net volume. It's running for almost two months now. There is a clear sea sk5000 filter as well. The filter roller gets pretty dirty. It's a full zeovit system. 9 fishes at the moment no coral (2 clownfish, 5 really small anthias, 1 baby blue tang, 1 mids blenny). The skimmer never really worked in front of the start of the tank. It has nice microbubbles but no real foam. I pulled off the filter roller yesterday and still no foam. What might be the cause of this? Thanks