The NaCl is a very weak restrainer. Its main use in fine grain developers is as a silver halide solvent. Remember, the first fixer for photo emulsions was brine. You don't want iodized salt because iodine is a stronger restrainer than bromine IIRC. You may be able to find the article "Salt to Taste" in the Photo Techniques back issues at www.phototechmag.com.