Filter media question

I was dissatisfied with the size bulk of the filter box I bought when
it was installed in the 1/2 barrel setup, so I made my own, which I
belive will work just fine, but my question is what kind of media
should I use. The typical foam type or the nylon scrubber pad stuff.
The filter box was made from an old acrylic hex shaped aquarium that I
cut down to 5" in height. I have bio media already for the bottom
section of 2 1/2 to 3" height, and now I need the filter pad material
for coarse and fine filtering on the top, so I can make a filter pack.
In the mean time I cut up and pieced together my old 6" x 12" filter
pad material. I installed the pump so it is attached to the outside
of the filter box, so it gives me easier access to the lid without
having to fool with the pumps discharge line. The lid is comprised of
the upper finish trim of the original aquarium, with a 1/2" mesh
(aquatic diamond mesh) grate, retained inplace with 2 stainless
steel snap action latches.

I should be able to just unsnap the lid, and lift out the "filter
pack" without even having to remove the box from the barrel half.

How is the carbon impregnated and or the special resin impregnated
pads for removing ammonia......is it a gimick or does it work.
Petsmart has a couple of different types in 10 x 18 sizes.

Would a layer of ammo-chips or carbon between the filter pads do any
good?

Any suggestions appreciated.
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