The only reason you might realy need carbon is for after medicating the tank if you want to quickly remove the medicines. However, even then it isn't necessary as most meds are biodegradeable and break down within a short time. Otherwise, the remnants are removed during water changes anyway. If you still need carbon for whatever reason, I'd just go for the cheaper or more practical of the two as they aren't realy important for your fish' well being. As for getting rid of ammonia, if it realy does this, it will destroy your biological filtration as the good bacteria use ammonia as food. Carbon eventualy stops working - if this were to occur and you forgot to replace it, you would have a major ammonia spike and re-cycle as you'd have no biological filtration (good bacteria) to convert the ammonia to nitrIte to nitrAte. You are better off with no carbon or similar products at all.