Betta Fish Fin Rot
If you notice your Betta’s fins are withering away and disintegrating (and there aren’t any obvious causes like aquarium mates attacking your little guy), you most likely have a case of fin rot.
Fin rot is a condition caused most commonly by dirty water. Bacteria blooms when your Betta’s feces and uneaten food accumulate. So make sure to keep to a regular water cleaning schedule. Also make sure to keep your Betta’s water at the tried-and-tested optimal temperature as I talk about in my book.
Try to detect and treat the condition early. You see, the good news is that your Betta’s fins will grow back.
Apply a product called “Neosulfex” by Aquatronics (available at almost all pet stores that sell aquarium supplies). It should take about a month to work, so be patient. If Neosulfex is not fully effective, also use a product called Jungle Fungus Eliminator.
Meanwhile, keep your sick Betta separate from your other fish, since fin rot is contagious.