You can keep the sponges if you want. I know of people who sandwich their carbon between two sponges in the first chamber, put Live Rock rubble in that netting that oranges come in, and in the third the heater and pump upgrade. If you don't have one I suggest a surface skimmer attachment for your nancube. I don't want to start trouble but there is a website that is strictly nano oriented if you are interested. nanotank.com
Tim