Brett Miller wrote in
:

I know what AC is and how it works. What exactly does it do in an
aquarium? What is it adsorbing? Not the ammonia, NH3 or NH4 is it?
So what? Color, odor?

Colour, odor, some plant nutrients... lots of stuff, but no not NH3/4. Use
Zeolite if you want something to absorb ammonia.

Active carbon is not really necessary, it is just a polisher, but it can be
detrimental if you are keeping live plants.