It sounds like it may be columnaris, true fungus, or slime disease. Here are the symptoms for each illness:

Columnaris: Fuzzy, cotton-like substance attached to body (looks like fuzz or lint), clear or white stringy material hanging from the body, erosion of the gills, heavy breathing, pinholes appearing in fins. Usually effects the mouth or head region. Also may appear as yellowish, white, or greyish areas on the skin, often surrounded by redness.

Treatment: Columnaris is a gram-negative rod bacterium, and should be treated with an antibiotic that is effective against gram-negative bacteria or a broad-spectrum antibiotic. Kanacyn (Kanamycin sulfate), Spectrogram (Kanamycin sulfate and Nitrofurazone), Maracyn, Tetracycline, or Furan 2 (Nitrofurazone) are all good choices.


(True) Fungus: Gray or white slimey looking material on the skin, may eventually turn into cottony-looking growth (distinct hair-like filaments).

Treatment: Maroxy


Slime Disease Excessive slime coat mucus production, white stringy strands hang off of body. Slime disease symptoms can also include frayed fins

Treatment: Malachite green


I'm leaning towards slime disease but read up on each of these illnesses and figure out which one your betta has. The damaged fins could also be fin rot (caused by poor water conditions) in addition to something else.


Though sometimes harder to keep up with than we originally thought (I have 20+ bettas in dire need of water changes today.. ), it's really important to keep up with water changes. The larger the tank your betta is in, the more time you can take in between water changes. If he got sick in four days, it makes me wonder how large his tank is. It's also a good idea to add a bit of aquarium salt and a drop of aquarisol as a disease preventative. None of my bettas have come down with any illnesses since I've started doing that.

Good luck!!