A liquid biocide containing stabilized chlorine dioxide and hypochlorous acid for various uses, including use as a teat dip or dairy animals. The stable, prophylactic biocide consists essentially of 0.10-20.0% by weight of a chlorite salt, 0.1-3.0% by weight of an acid, 0.10-2.0% by weight of an alkaline agent, and the balance water. Chlorite salt reacts with the acid to form germicidal chlorine dioxide and hypochlorous acid. The acid constituency and the alkaline agent constituency regulate the pH of the solution such that the biocide is stable when mixed for a period greater than two months. The present disclosure also includes a method of producing a stable, prophylactic biocide for dairy cattle, the method comprising 0.10-20.0% by weight of a chlorite salt, 0.10-3.0% by weight of an acid, 0.10-2.0% by weight of an alkaline agent, and the balance water in a container, and sealing the container. In the method, the acid and alkaline agent constituencies regulate the pH of the solution such that the formation of hydronium ions from the acid is correspondingly regulated to stabilize the solution for a period greater than two months from the date of sealing.