Do you mean that you skimmer has been set the same way forever and it just now started producing extra wet nog? If so, it could be due to anything that has been added to your tank. Too many proteins added via food, dead fish, chemicals, etc. can all cause the skimmer to go nuts and a lot of times completely overflow.

But if you just want your nog thicker... like Jolson said, adjust your skimmer. Each skimmer adjusts slightly different.