Fin Rot occurs when the Betta is distressed due to poor water conditions, overfeeding, uneaten food, overcrowding or rough handling. If the water is not changed regularly, the leftover food particles and feces will decompose and contaminate the water. If there are too many Bettas or too much food in the tank, even regular water changes may not prevent the disease. The resultant stress on the Betta lowers his immunity, thus making him very susceptible to attack from the bacteria present in the water. Only in rare instances will Bettas develop Fin Rot when a tank is impeccably maintained.