Cause

• Fungus on a betta fin is usually caused by body fungus resulting from poor water conditions, parasites or injuries, according to Healthybetta.com.
  
  

Signs of Fungus

• Signs of body fungus include white or gray-colored, cotton-like balls on the fin and body. Signs of fin fungus include stringy gray tufts or fuzzy material, which attacks the fins.
  
  

Effects

• Bettas with fin fungus will be lethargic. The fins may disintegrate and reduce the betta's ability to swim. The betta may also lose its appetite.
  
  

Treatment

• Treatment options typically include formulas that contain methylene blue, such as Jungle Fungus Guard, Mardel Maroxy and Aquarium Pharmaceuticals Fungus Cure. Aquarium salt also aids in healing the fungus, according to Healthybetta.com.
  
  

Prevention

• To prevent betta fin fungus, change your tank water frequently and increase water circulation.