Radiative and Auger decay data have been calculated for modeling the K lines in ions of the nickel isonuclear sequence, from Ni(+) up to Ni(27+). Level energies, transition wavelengths, radiative transition probabilities, and radiative and Auger widths have been determined using Cowan's Hartree-Fock with relativistic corrections (HFR) method. Auger widths for the third-row ions (Ni(+)-Ni(10+)) have been computed using single-configuration average (SCA) compact formulae. Results are compared with data sets computed with the AUTOSTRUCTURE and MCDF atomic structure codes and with available experimental and theoretical values, mainly in highly ionized ions and in the solid state.