I googled it so i dont know. If you put a picture up people might be able to help.
Description: Fin rot is one of the most common, and most preventable, diseases in aquarium fish. It is caused by several types of bacteria, and often occurs concurrently with other diseases. It can usually be cured, but if left untreated, it can kill the diseased fish and infect all the others in the tank.
Symptoms:
Fin edges turn white
Fins fray
Bases of fins enflamed
Entire fin may rot away
The fins begin to fray and get ragged, becoming shorter over time. Usually the edges look white, and may even develop a fuzzy growth due to secondary Cotton Wool infection. A the disease advances the area may become red an inflamed, with bloody patches appearing as more of the fin is eaten away.