[Regloh]

I am using whatever the Eheim came with... If I were to start again with an empty filter I would probably try to split it between a course sponge on the bottom and filter fleece on the top.
I only ran carbon for 1-2 weeks after the new filter install, in case something nasty came with it.
I am in the planing stages for a small (probably 10g) shrimp tank, and am entertaining the thought of a HMF (Hamburger Mattenfilter) which is just a sheet of filter sponge with a power head behind it, but that may still change.