Ok, thanks! I'll go to Walgreens today to see what I can find!
Today he's still active and trying to chase the "other fish" aka his reflection away, but he's still not flaring. There's some more fuzz coming off the top of his body, it looks a bit stringy, and there's what looks like a ball of the white fuzz on his dorsal fin. Hmm. Should I be suspecting fungus? His fins were clamped while he was sleeping, but when he's swimming around they're all flowy like they normally are.
EDIT: He keeps taking short rests on the very bottom on the gravel. Is this bad? His fins are clamped while he does this and then when he swims up for air and chasing his reflection, they're normal again.