Ok, I thought I understood filters pretty well, but now after reading various threads and articles I feel like I'm more confused than ever. Could someone explain or point me to an article that can really help me get this. I have a Whisper 40i filter, and inside it has a plastic piece with bristle things, a mesh and carbon inside that. First, what is the bacteria growing on? Second, should I change the mesh and carbon each month? Third, should I keep any of the old mesh in, or is it all just junk? Hopefully that all makes sense. Thanks!