This is actually called "dissolved organics,and waste.It is a sign that your skimmer s working.But if this wet substance is all you are seeing comming from the skimmer,it is not working at it's peak performance.When properly adjusted,the skimmer should be producing a brownish colored "dry foam" that will rise out of the skimmer and overflow into the collection cup. Try increasing the air,and turning the water flow all the way down...This will increase the contact time between the water and the micro bubbles.....