A biocidal composition includes glutaraldehyde, alkyl-based quaternary ammonium, benzyl-containing quaternary ammonium, and an isothiazolinone composition. The biocidal composition can further include water, alcohol, or a magnesium salt. Such a biocidal composition finds particular use in treating fracking fluids. The biocidal composition can be mixed with a treatment fluid prior to pumping the treatment fluid through a well head.
