Aquarium Pure water use MBR10 DI Resin.

“DI Resins” are synthetic porous polymers that “deionize”. There are two basic types of resins. One is a “anion” exchange resin. Anions are negatively charged ions such as nitrates and nitrites. The other type of resin is a “cation” exchange resin. Cations are positively charged ions such as ammonium.

As an example of how a resin works look at the cation filter media out there which claim to remove ammonia from the aquarium by exchange with sodium in a resin bed. Cations include sodium, ammonium, potassium, magnesium and calcium. The claim is that these resins remove the ammonia as ammonium.