If I remember correctly (it has been a while since I cleaned mine out) most of mine, if not all, have a fine sponge filter.
I removed the carbon, never use it, and filled all the trays with ceramic noodles with the top trays having coarser sponges.
When I clean the filter out I rotate the trays (the one on the bottom goes to the top) so the noodles get to live in different levels over time.
If I find the time (and my husband to help) I might pull mine apart so I can see what is where, and take photos.