Gazer,
I'm certainly not glad to have oddities with my little guy, but I am glad we're experiencing similar symptoms at roughly the same time - hopefully we'll be better able to sort it out having more than one "test subject".
In regard to the rust theory, there are no metal elements in Gir's tank and we have copper piping throughout the house. This doesn't eliminate rust as a possible culprit, of course, but it may lesson the concern a bit.
In the last 24 hours there has been dramatic improvement in Gir's condition - the stark redness is now isolated to a single toe and there's only a slight pink tinge to the other toes on the front feet and no noticeable discoloration on the back feet at all. The changes I've made in the last 48 hours are:
1. I've switched from using API Stress Coat Plus to API Tap Water Conditioner, which contains no Aloe Vera or other ingredients intended to replace slime coat or reduce stress.
2. I've completed two full water changes.
I notice that you're using Prime as your dechlorinator - could it be that the Aloe Vera is actually irritating them? I've read that some axies are super sensitive to even supposedly beneficial additives (though I can't for the life of me remember where). Might be worth a shot switching to a simple dechlorinator and seeing if there's any improvement.
Glad to hear Aristotle is doing better.