I see that the bubbles are being created. It also pushes some foam to the top of the collecting cup. However the foam is very clear and it does not extract waste as it used to be. A thin layer of brown sediment is also forming on my substrate once every two days. From the bubbles creation the skimmer seems to be working fine. But is there a blockage or something that makes skimmer not to collect waster? How do I ensure that the skimmer is working? This is four months old Won brothers skimmer.