Time-lapse view of a dead fish, to test the old saying that a "fish rots from the head." Does it really? Discussion of video at
Fin rot or tail rot (melt) is probably the most common betta fish disease. It’s often confused with tail biting, resulting from boredom, and tears on sharp tank decor.
This is a rare protozoan disease that causes a cloudiness of the skin. The best treatment is with copper at 0.2 mg per liter (0.2 ppm) to be repeated once in a few days if necessary. Acriflavine (trypaflavine) may be used instead at 0.2% solution (1 ml per liter). As acriflavine can possibly sterilize fish and copper can lead to poisoning, the water should be gradually changed after a cure has been effected. Raising the water temperature to 80° - 83° F for a few days has also been effective.
The next level of betta fish fin rot is:
Fin and Tail Rot in betta fish.
Severe cases of fin rot (fins just seemingly melting away and falling off in big pieces or when the rot is close to the body) should always be treated with an antibacterial fish medication like Sera Baktopur Direct or Tetracycline. Products like Melafix, Pimafix and Bettafix do not cure fin rot and may actually make it worse. To treat a betta with fin rot using aquarium salt, transfer the fish, a heater and some hiding places like real/fake plants to a separate or tub with treated tap water of the same temperature as the water in the aquarium (be sure to give the fish some time to acclimate to the 100% tap water)! Set the heater to a temperature of around 77-78 F – any higher will make the rot progress more quickly, and any lower and it might be harmful to the fish. Unfortunately, heavy medications have a lot of negative side effects like the possibility of bacteria eventually becoming resistant and the fish becoming extra stressed. Luckily, less severe rot (slightly ragged looking fins) can be treated with a combination of and aquarium salt, which has way less negative side effects. Try to keep an eye on your fish at all times to catch any cases of rot before they get too bad – that way you can prevent having to use medication! If you keep repeating this process for around a week and a half (any longer can cause organ damage in the fish), you will likely see some good , and maybe even some fin regrowth! You can now carefully acclimate him back to his regular aquarium. Be sure to keep an eye on the fish after this, though! If it gets fin rot again, you may want to take another look at the tips to prevent fin rot below.