Jerry, thanks for the help. Here are a few more tidbits I just got:
Originally Posted by Gerald C Koch
* The purple coloration of the used developer was gone this afternoon; it was water-clear.
* A clip-test from 20 minutes ago with normal temp/time/agitation/stop/fix/wash gave identical results to yesterday, so the dev did not degrade noticeably over 22 hours.
* I divided the used dev into three parts, and put the three ion-producing chemicals into each. This was not measured; just a little bit in each, which was undoubtedly far too much. The Ferrous sulfate gave light purple, and the Ferric ammonium sulfate (FAS) produced a dense purple. Copper sulfate gave no color. So I suspect the colour is due to the FAS.
* I put a little FAS into a beaker and added unmeasured quantities of each chemical in the dev. Nothing produced a purple, so maybe pH matters and I should measure quantities correctly.
The FAS from the Formulary was labelled "Ferric Ammonium Sulfate", but the CAS-number on the packet is for Ferric Ammonium EDTA. It came as large crystals covered with white powder. When broken up, their internal colour is slightly pink as is pictured in Wikipedia here, so I think I have the correct stuff.
Well, assuming I don't have the erroneous EDTA in there, it looks like the Fenton reaction is not an issue over the time-frame of one day.