Freshwater ammonia remover is zeolite, it is a mineral which in freshwater can exchange sodium ions for ammonia, since saltwater would have more sodium then ammonia it will not work, zeolite can be recharged by putting it in strong saltwater, it then releases the ammonia back. In saltwater zeolites are used but they only work as a bio media and culture bacteria. I would agree with the advice to add a skimmer as the best remedy.
I'm still not sure what the answer is if I can use freshwater ammonia remover in a saltwater tank? I'm new to this site and don't know if I missed the answer but would appreciate someone's opinion, Thanx Kevin