Zeolite absorbs things including ammonia and medication. It removes the ammonia before the bacteria have chance to use it. With no food, the bacterial colonies will decrease in number. The danger then is that the zeolite gets full and stops working, and the bacteria numbers have dropped too low to cope so the tank goes through a mini spike while the bacteria increase again. If zeolite is used, it must be replaced before it gets full, forever. Using bacteria to remove ammonia is a lot cheaper.
I wouldn't use carbon either. Carbon's only use is to remove medication after treatment has finished. It is better to use the space in the filter for sponge or ceramic media.
Okay could you please help me with how to set out my canister filter then? So on the bottom I have thick filter foam, second I have ceramic rings and plastic biological filtration, top I was going to have zeolite and poly pad. Is this a good setup or would you reccomend something different?