Gerald, your knowledge and experiance is always welcome. Unfortunately many raw chemicals (not only DTPA) are increasingly difficult or impossible to get, e.g. Triethanolamine, Dimezone S or Boric acid, or ridiculously expensive in useful quantities. I've seen the recipe you posted above before, but many of us - including me - can't make it ourselves. So we have to buy the ready made product - Xtol in this case - or use simpler recipes. That's why I posted the link to the instant Mytol. I also use low grade chemicals, e.g. "bubble ex" sodium sulfite and had no problems with the developer in use since 12 months. The double strenght stock dilution I made even had a light yellow color at last but still worked fine. I guess storing the developer in small glass bottles helps a lot to keep it working.