Okay,
Agreed you biff the black stuff which does look to be carbon.
One more question, was the layer of what to be filter wool which is sitting under the carbon there when you first got the filter?
I use the sintered glass, causes a lesser flow to what you would get using two baskets of the ceramic noodles.
Fish guy, The sponge around the outside of the baskets is the stock standard sponge the filter comes with and is not the issue. I believe the problem lies with whatever other wool pads are in the baskets and that they are blocking and slowing the flow.