i have a Bak-pak skimmer that is about 6-8mths old. the collection cup has always been full on a daily basis. it pulls a lot of skimmate out..nothing has changed in the tank, but it has stopped collecting lately. it will go for 2 weeks and not even be full. the problem seems to be that all of the bubbles are coming up around the sides of the cup instead of going up the tube into the cup. the air tube is clear of debris and the skimmer is level. i don't understand why it has quit working. i have cleaned the pump and the skimmer thoroughly. the problem seems to be the bubbles coming all around the cup. any help?