I just bought the protein skimmer for my bio cube last week. I'm not exactly sure if I'm using it correctly as this is my first fowlr tank. I pulled out the main filter and replaced it with the skimmer unit, which I'm sure is right. The main question/problem I'm having is how high to I want the bubbles to be, and the only thing that seems to be collecting in top is foam. Is that "foam" what is supposed to be in there or what? Sorry if this makes no sense, I'm still a newb.