Interesting formula. Until you explained the presence of the Disodium Phosphate, I was at a loss as to its purpose. And another oddity that appears to me is the use of Metol with sodium sulfite in anhydrous form rather than dessicated as seems to be, by and large, customary. The anhydrous seems to be primarily used with hnydroquinone. (Ron must be rubbing off on me a little.)

Great recipe.
Thank you for sharing it with us.