Hey, thanks to everyone who has chimed in!
I was iffy on the charcoal thing and since I'm overfiltered anyway, I removed it. I was under the impression that it was inactive and simply a surface that was colonized, but figured it was worth a go since I've got nothing to lose by removing it.
I did raise the temp two degrees fahrenheit to 79º and he is more active and not as green/stressed-looking as he has been lately. For all I know, the two 300watt heaters were struggling to keep the temp up in the new wintery nights. With a wider margin for dropping in the comfortable zone, his stress should be lessened. Not that I've ever noticed the temp swing at all, anyway.
Water changes at no more than 50% per week. I do not trust the city water quality reports any further than I trust the IRS, and it is always obvious when they overload the tapwater with chlorine. I bump the Prime dose those weeks. On the national map, it is clear that my city is on the government's list of extermination by fluoride, so I drink well water now, but I have no way to haul that much water to my house. So I prepare water for my tank bucket by bucket, aerating as much as possible and dosing with Prime as it fills and matching the temp almost flawlessly.
He ate the Prazi-Pro-soaked Massivore for three days and I scrounged up enough change for a vitamin block as my LFS guy uses to treat HITH. Whether or not it was actually needed, I'll never know. Treating HITH seems to be as multifaceted as causing it!
His two tiny holes have closed over completely. Thank you for renewing my hope for Oscars.