The circular floor scrubbers that cleaners use with floor buffing machines
would probably do the trick.

Yep, they will.
Just cut them up into smaller pieces and toss in the bottom of the
filter.
If you have anything like a Dollar Tree store, you can get packages of
scrubbers that work too.

Also, hair curlers that have the hairy points all over works too.

I also threw small pieces of old PVC pipe in my filter media.