Charge exchange recombination (CER) spectroscopy in the visible spectrum is used to measure the radial ion density distribution of impurities in the core plasma of DIII-D. The radial profile of the effective ionic charge, Z_eff(r), is subsequently calculated from the impurity densities and the electron density of the plasma. The CER measured radial distributions rely on a calculated neutral beam attenuation radial profile, which is confirmed by independent measurement. This technique, which determines the deuterium density of the neutral beam by coupling measured beam D_α emissions with a time dependent collisional radiative calculation, will be described. The CER derived absolute density/concentrations of carbon are verified by comparisons with the spectrometrically measured visible bremsstrahlung emission of the core plasma, which is proportional to Z_eff. Conversely, the seeded neon concentration is overestimated by a factor of 1.7 by CER. This correction is shown to be caused by the enhanced direct capture into the upper level of the measured visible neon transition (Ne X n = 11 to 10, 5249 Å) from excited (n = 2) beam atoms. Owing to several problems, including line radiation contamination of the spectral region of the diagnostic, the standard Z_eff(r) derived from inversion of line integrated visible bremsstrahlung emissions does not provide reliable profiles, but rather a measure of the average impurity content. The Z_eff profiles are found to vary considerably in shape and magnitude over different operational regimes, confirming the need for accurate profiles.