Sorry to hear about your typhoid Martin. I got lazy and didnt quarantine a fish my LFS sold me and he same thing happened.
It sucks but caught early you can more than likely cure him:
1). Hard to positively ID Hith (lateral fin disease) w/o better pics.
2). You can put your Carbon back in, any causal relation has been debunked.
3). The actual cause is a nasty little protozoan parasite that exists in low levels in the digestive track of most perciform fish.
4). It's a parasite and you need to medicate accordingly.
5). The correct remedy is metronidazole, administered via medicated food or added to water or both.
6). You can safely ignore all the anecdotal advice and holistic remedies out there with one notable exception: water quality. There is strong correlation between the parasites spread through the rest of the organism and bad water quality and/or poor nutrition. The caveat being that correlation is not causation.
Hope that helps
Please forgive any sloppy language or typos; it's late- Lousy week & i'm burnt but I wanted to get you some useful info ASAP