fluid bed problem

[jim680t]

I build a fluid bed as per instructed, all I get is a little bit of air coming up around the outside edges of the F B no bubble, just dust, I used a coffee filter for the screen at the bottom of the cup, the more air, the more dust no bubble what kind of media are we suppose to have as a filter, I've reduce the size from 3 inch to a two inch same thing,what I'm I doing wrong.