Abstract The effectiveness of two processed samples of New Zealand mordenite for possible use in removing total ammonia nitrogen (TAN) in aquaculture application was studied. The percentage reduction in TAN concentration in 100-mL solutions held on a rotating shaker increased linearly with greater mordenite application rate, while the amount of TAN removed per gram of mordenite (adsorptive efficiency) declined. At a TAN concentration of 200mgL−1, both mordenite samples had an adsorption efficiency of about 8.7mgTANg−1. Ammonia removal and adsorptive efficiency decreased with increasing salinity up to 30gL−1. In aquarium tests with less vigorous mixing, mordenite at concentrations equivalent to 10 to 500kgha−1 in ponds removed only 1 to 8% of TAN from water. Mordenite and other zeolites are not useful for removing TAN from ponds. The New Zealand mordenite was of good quality and like other zeolites could be used for other applications in aquaculture such as small, intensively-stocked transport and holding units for aquatic animals, water recirculating culture systems, and possibly as a feed additive.