I've been a Betta enthusiast and breeder for more than two decades, but it is important to note that I have no medical or veterinary experience or education. While these cures have been successful on my Betta fish for the last 20+ years, this information does not take the place of a licensed veterinarian.

If you are not careful, your Betta can be exposed to a number of diseases and illnesses. You will usually want to separate your diseased Betta fish. This will allow you to safeguard the remaining fish in case the illness is contagious. Try to utilize a portion of the water in his own current tank and let any new water sit for a minimum of 6 hours to avoid a sudden change in temperature which may result in a shock to his system.

Furthermore, as a general rule make sure to scrub your hands with an antibacterial soap after submerging your hands in the water, to avoid spreading the illness to other fish (and in case it's Tuberculosis, so you do not get - see below).