Vertex Omega 150 - not skimming as usual

[kamloops_reefer]

the skimmer appeared as if it was going to work properly after I had taken it all apart. I not have the riser tube almost completely closed, while sitting in a steady 8" of water. I've had this skimmer running twice before without this concern. it almost seems as if the bubbles I'm getting are different, almost as if anything that spills over into the collection cup is watered down, rather than thick and dark (as before)