I just improvised a mini sump with a 10 gallon tank. I have about 9 inches of water in it, the PSK-200 and the return pump. I've got the water level stable, but as soon as I turn the skimmer on, the air bubbles go up and the collection cup fills with water in seconds. I've turned the blue knob on the "L" position. I'm assuming that "L" stands for "Low" and the "H" on the other side is for "High". Can somebody help me with this problem? I need to turn this on and make it work properly ASAP. - Magnus.