Why Is the Betta Water Green?
Fur Coat Syndrome and Betta Care
(The First Tank Guide)
"Fur Coat Syndrome" is a dermal bacterial infection (though most fishkeepers would consider it a fungus because it looks fuzzy). Bettas are very susceptible to this ailment, though other anaboitoids or labyrinth fish could catch it (it does not seem to affect unrelated fish).
It is generally characterized by discoloration of tissue, particularly the fins, to a dark brown or black and a grey or brown 'fur' or mold over the body, usually starting across the back and at the base of the fins and rapidly spreading to cover most of the body.
Loss of appetite and listlessness are also common signs. Though this disease can be readily prevented by keeping your Betta in warm enough water, providing them with a good diet, and setting them up with enough space (not keeping them in a bowl or vase), it is highly contagious, and can be spread through the air over 100 yards (possibly more).
"Fur coat syndrome" is almost always fatal within 30 hours of the first signs or symptoms. In cases where you know that one fish has caught this disease, using a targeted Betta antibiotic can reduce the risk of contagion to other fish. This is why the Betta water in many pet stores is often dark blue or green in color - shipping is very stressful to the fish, and often, even under the best care, the fish will drop below 74° Fahrenheit while shipping, making them very susceptible to this disease, and keeping them in a targeted antibiotic solution greatly increases the fish's survival rate in the face of this illness.