Well, that futile - I came in to check him this morning and he was dead.

At this point, I'm just going to give up on Ceratophrys, at least for the next few years. I have no idea what could possibly be wrong, I've tweaked and altered every possible aspect of their care, and they still die within 2 months.

Unless anyone has alternative suggestions, my best guess is that it's something about this apartment, some toxin or noise or pollutant that only bothers Ceratophrys. Because at this point, that's the only common ground in all the frog deaths.