To set up the Penn Plax Cascade aquarium canister filter you need to clean it thoroughly and dry it before setting up the filter system. Next, you are going to set up the filtration media exactly in this order: Mechanical media basket goes at the bottom, chemical filtration basket in the middle, and lastly, biological filtration basket goes on top. (make sure that the tube of media basket gets in line with the tube in the previews media basket) Add the filter guard on top and you are ready to seal the tube from the basket to the head of the filter with the O ring. Set up the header and you are all set.