As an experiment I DIY'd a Fluidized bed filter and was wondering what the fluidized sand is supposed to look like in motion. the top half of the cylinder has bits of sand constantly moving, the lower half resmebles a fast quicksand like motion. is this right? For test media im using black silica sand and some small glass beads from the craft store( kinda look like mini ceramic cylinders) to help move the sand and hopefully retain BB. I also have an air stone in there to inject oxygen. Do you think that would help? Also how well does smooth surfaces (like the glass beads im using) retain BB?