Q: R wrote,
A: Fin rot is caused by a bacterial infection. Different types of bacteria are usually present in the water but dangerous forms of bacteria generally strike fish that are already stressed. The most common stressor is poor water quality. Poor water quality is just a general term and can consist of one or several problems ranging from fluctuating temperatures to the presence of toxins like ammonia or nitrite.
The great majority of water quality problems cannot be recognized by the naked eye. Water that appears crystal clear may contain lethal levels of common toxins. The most common and one of the deadliest toxins, ammonia, can be deadly in even low doses and will have no color, smell or texture that you will recognize. It is also likely the greatest threat to fragile betta fins. The only way to know if your tank is free of toxins is to test your water frequently with an aquarium water test kit. There are several types to choose from including inexpensive dip stick tests (not very accurate but simple to use) and reagent test kits (very common in the hobby). Most local fish stores will test your tank water for you free of charge if you bring in a cup full.
When treating fin rot, the first thing you must determine is the cause. Begin by checking your water’s temperature, pH level, ammonia, nitrite, nitrate, gh and kh. These are the very basic water parameters you are dealing with in a basic fish bowl or tank. All aquarists, whether they have a 1 gallon or a 100 gallon tank, have to deal with these parameters. To learn in detail about each parameter visit “All About Water.” Once you have determined the cause of the problem and have corrected it you can then begin to treat your betta’s fin rot either though the use of good clean water or medication in severe cases. To learn more about treating this fish illness visit “Fin Loss vs. Fin Rot.”