you need to pull out the impeller and clean that also, it is located in the middle of the box where the tube goes. as far as filters you can get a good deal at wallmart also those boxes are for substrate and are optional
Whatever you may need like biowheels, fiter cartridges, impellors or any other replacement parts...you can get them at bigalsonline.com. It's a huge site with everything you need for aquarium's aside from big tanks.