Agfa used to recommend mixing up Rodinal with a weak sulphite solution if you needed to prolong the life of a working solution this also helps give finer grain.
As Ian points out mixing the Rodinal with a sulfite solution will improve the grain. Years ago a 9% solution was recommended as the resulting developer would be close to the recommended sulfite content for such developers as D-23 and D-76. However, it now known that maximum halide solvency occurs around 80 g/l so a weaker solution would be better. When using this method development times should be shortened by approximately 20%.
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