A method of stabilizing a solution containing a 3-isothiazolone complex of the formula ##STR3## wherein Y is a hydrogen atom, an alkyl group of 1 to 18 carbon atoms, an alkenyl or alkynyl group of 2 to 18 carbon atoms, a cycloalkyl group of 3 to 12 carbon atoms, having a 3 to 8 carbon atom ring, an aralkyl group of up to 10 carbon atoms, or an aryl group of up to 10 carbon atoms;R is a hydrogen at