My first experience with fin rot was with two guppies that I had a few years back. their tails looked like some of the other fish had been using them to supplement their food. After doing a bit of research I found out that Fin rot, a common ailment of aquarium fish is fairly easy to spot, and if caught early, can be treated right away. The first signs of fin rot appear around the edges of the fish's tail or fins, and are milky white patches. As the disease progresses, the fins and tail start to look ragged, because the disease is starting to eat away at the tissues. If fin rot has effected the tail, it can work it's way into the fish's body.
It is important to diagnose this condition right, some fish have frayed fins naturally. Guppies tend to nip each others tails, and this can appear to be fin rot. If caught early, you can treat the root cause, letting the fish heal itself, rather than having to treat the whole tank. This is a bacterial infection, and several different kinds of bacteria can cause fin rot. One of them is Flavobacterium, others are Aeromonas, and Pseudomonas.
Fin rot can be treated in three different ways, changing the environment is one of them, and this can sometimes be what the problem is. If the tank is dirty, or has baterial components, then you need to change the water a couple of times, thoroughly cleaning as much of the debris and feces as you can. Replace all the filters, and make sure that you also clean the gravel.
There are a number of antibacterial treatments, and if possible, move the infected fish to a separate tank, then use the treatment as directed. There are a number of antibiotics available, both in an over-the-counter form as well as from a fish doctor. Again, it is important to follow the instructions carefully.
If you can catch fin rot early, then you shouldn't need to use antibiotics. Unfortunately for my two guppies though it was a little bit too late and I lost them both