when is something that is plastic, small and collectible not an ideal filter media? When it is plastic forks, plastic army men, plastic shipping strapping, PVC pipe chips, bottle caps, styro peanuts ------- etc. etc,
The reason is-- surface area is only ONE of the needed parameters that makes 'bits of things' suitable for biofilm cultivation.
Beyond pure potential growing area, you need:
void space
non packing properties/characteristics
non trapping properties
Keep looking!
JR