Betta Fish: Fin rot or something else?

Hi everyone! I've been an avid keeper of bettas for about 8 years and have had extreme success treating fin rot with jungle fungus clear in the past, which unfortunately looks to be discontinued or out of stock everywhere I look. A friends daughter "gifted" me this cutie who has (what looks to be) one of the worst cases of fin rot I have ever seen. However, in the past I've seen black dead fin or melting along the body, but I'm not seeing that much with him…? He lives with 10 cherry shrimp in a heavily planted 13 gal tank and I've never once seen him nip his fins or lose a chunk quickly. Water parameters are all in check as well and I have proper oxygen input. I test my water every other day, if not daily. Sweetest boy; eats a ton and is very lively. I've done the typical 70-80% water changes, dropped temp to about 73 (I know it's a little low, but the negative gram bacteria struggles to grow in lower temps from my understanding), and dosed aquarium salts. However, he hasn't gotten much better. I've now hospitalized him and have used kanaplex, which is a medication brand new to me. I've seen many people in this sub have a ton of success with it, so I figured I'd give it a go. My question is; what should I be looking for? Any signs of regression that I should watch out for? I've never treated a fish this far gone, only mild cases that I've caught early on. He's only on his first dose but I don't see any clamping or signs of stress; maybe a little lethargic or the occasional quick dart but that's really it. I've got almond leaves on the way for some healthy tannins and a good hide for him in the hospital tank. Any advice is extremely helpful as I would love to see this boy in his prime again! (He's about 6 years old!)