Aww man, just realised one of my fish is starting to get mouth rot :c

For anyone who is interested in keeping fish,
Here's a tip.

The best research you can do (other than appropriate tank size, etc)

Is to go to your local pet aquarium, find out every medicinal product they have for fish, and learn what each of them does and when to use them.

Sure, there's no 100% guarantee that you're fish will recover, but the quicker you can figure out what you need and for when, the better,

Sure, there are many great fish keeping books that can tell you about stuff, and they're still worth a read,
But often, not all the medicines will be available in your area