Shawna, first, keep up the water changes. I also just want to make sure that it's an actually ammonia smell and not the smell of rotting organic debris? If it's a more organic smell, don't worry too much. If it's ammonia, I really think you should check your ammonia levels.
As for carbon in general, I REALLY hate it. You have to change it about every 2 weeks for your normal everyday stocking which seems like a really big pain to me on top of it not being necessary to even have carbon. I cut open the top of my filter cartridge, remove as much as the carbon as possible, rinse, then put it in my tank. Then, I don't ever have to buy a cartridge again either.