There are at least 15 known diseases that can affect your bettas. Although most of them are fairly infrequent, there are three that you definitely need to know about so you can initiate therapeutic action immediately. These are mostly non-lethal diseases but can cause discomfort and seriously impede their normal functioning.
Fin Rot
This is probably the most common condition found in bettas. Fin rot usually follows fin burns, and is relatively easy to treat when compared with the rarer conditions such as that which causes dropsy, for example. Fin rot is usually lethal to most fish but because bettas are able to take in atmospheric air, they can survive until the condition is treated. The treatment itself is fairly straightforward: because the condition is caused by polluted water, frequent water changes can effectively deal with the problem. You can also add a little salt to the water to contain the infection and prevent it from spreading. Bettas are typically tolerant to higher salt levels than most other aquarium fish, so you can use one tablespoon for a minimum of one gallon of tank water.
Ich
This is a protozoan infection that can be dealt with swiftly. The symptoms are usually white spots that appear in groups, and the pathogen primarily affects the gills. Again, since bettas can take in atmospheric air, they may survive longer than other fish with this condition but your bettas may die if left untreated for this indication. However, treatment is always advised as soon as you notice the white spots starting to appear. The treatment involves increasing the water temperature to 90 F and maintaining that temperature until the infection subsides. Aquarium salt helps here as well, as it can prevent the spreading of the disease as effectively as the temperature change.
Velvet
This is another protozoa-based condition that can be treated much the same way as Ich; raising the water temperature and adding a measure of salt to the aquarium can rid your bettas of this infection in a short period of time. Frequent water changes are also advised as a treatment step; in addition to having therapeutic value, changing the water more frequently than you normally would ensures infections such as Velvet don’t recur and cause discomfort to your pet bettas.
These three conditions crop up fairly often with bettas, and knowing the steps to take can ensure their health is restored as quickly as possible.