A method of controlling or arresting the rate of depolymerization of a polymer composition during a biocide treatment, and use of such methods in oilfield and industrial applications. Also disclosed are methods of preparing a visco-stable application fluid containing a biocide in an amount effective to reduce bacteria count, as well as additive compositions capable of reducing bacteria count in application fluids while maintaining viscosity in such fluids. Also disclosed are methods of preparing biocide-containing application fluids with improved friction reducing properties, as well as related compositions.