Unfortunately, there really is no ideal way to remove nitrates chemically. Although, refugiums can help export nitrates and Phosphates, the best way to lower nitrates is to prevent them from being made by removing waste, uneaten food, etc. before it is broken down by nitrifying bacteria. A skimmer is usually the most efficient means to do this. However, in the interim, running carbon will also help.
Sulfur denitrifiers can also be used to break down nitrate to nitrogen. However, they also come with a set of risks if not used properly.