Update:
I've been doing 50% water changes daily. Decided not to medicate at all to begin with (the iodine scared me, and I wasn't sure about other medications. I also dropped the tank temp to about 77 F.
A lot of the white stuff that was on the plants is now gone. I'd say about 90% reduction.
I'd also say about 90% reduction in the white stuff on the fish.
He's still not eating like he used to. He'll take about 2 medium pellets per day now if not just 1.
Hopefully the tank/fish continues to improve.
Also.....idk what it ever was.....But.....I seeded my new tank with a piece of driftwood that I had previously had in the tank where my sick fish is now. It immediately started growing TONS of the white stuff. Thing is, I remember it doing this when I first got it, boilded it, then put it in the tank. It then went away, but I've had it on the fake plants since. I think it all came from that wood. I removed it from the new tank, and set it outside to dry out, and it looks NASTY. White stuff all over it. I'm throwing it away. Luckily, it doesn't look like any of it got on anything in the new tank.