Hello all.\n \nLong time Bak Pak user. Not too long ago I switched pumps to the Accela recommended on the Bak Pak Site. It is a lot stronger in terms of flow and air bubbles than the stock Rio.\n \nAnyway I would lower my collection cup to 1/8" or so under the water surface like I have been for years. A couple hours later I would come back and the water surface would be 1/4" - 1/2" below the collection cup with a 1/4" or so layer of foam between the cup and water surface. I would lower my cup again and once again the water would go lower. No matter how much I lowered my cup the water level would always seem to stay below it and the gunk would not enter the cup - it would stay on the water surface below it.\n \nWhat I finally figured out is all of the air bubbles flowing through the column of water need to go somewhere when they reach the top. The tight fitting lid on the collection cup was not letting enough air flow through. The Bak Pak only has four very small vent holes in each corner for this purpose. The cup was basically trapping air in the skimmer column preventing the gunk from entering into the collection cup.\n \nI simply took the lid off the cup and set it sideways across the top. It works great. The flow into the cup has increased significantly and nothing spills out or overflows. I've also run it for days without any lid.\n \nJust wanted to share this. It should be obvious but like many things isn't until you have to deal with it. May improve the performance of other brand skimmers as well.