Abstract: Aquatic nuisance species (ANS) in ship's ballast water are killed by permeating to equilibrium a gaseous mixture consisting essentially of, preferably, ?84% nitrogen, ?11% carbon dioxide and ?4% oxygen through ship's ballast water until the ballast water itself becomes (i) hypercapnic to ?20 ppm carbon dioxide, and, by association, (ii) acidic to pH ?7, while preferably further, and also, being rendered (iii) hypoxic to ?1 ppm oxygen. The permeating is preferably realized by bubbling the gaseous mixture preferably obtained from an inert gas generator through the ballast water over the course of 2+ days while the ballast water is continually maintained a pressure less than atmosphere, preferably ?2 p.s.i. or less.