My old betta developed this quickly, maybe fin fungus?

is this fin fungus??

Looks like a fungal infection to me. I would do a large water change asap.
What are your tank parameters? And tank size?
I’ll leave the rest to the more experienced. Good luck!

Add some salt to his tank.

You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.

It is a fungus but I would not describe it as fin fungus. In fact, it is in the caudal peduncle, and extends outwards including part of the caudal fin. Very likely started upon a wound in the body (even if small), and grew from there. At this time it s quite extensive but it should be stoppable.
The suggestion of salt + maintaining the absolutely best water quality possible is the the way to go and should result in improvement.

BleuTheBetta said:

Looks like a fungal infection to me. I would do a large water change asap.
What are your tank parameters? And tank size?
I’ll leave the rest to the more experienced. Good luck!

Click to expand...

Tank parameters are perfect, she is quite old and weak so that could be it. I did a large water change before this so maybe it’s stress? Her tank is a 30 gallon community tank. She’s in a quarantine tank in a salt bath for right now. She seems more active after a few days of treatment. Some of the dead fins are falling off.

Not stress, fugus. And then, the fish may be stressed. Also, fungal infections do not necessarily happen as a result of of age. Age cannot be changed, but a fungal infection can be cured.

FranciscoB said:

Not stress, fugus. And then, the fish may be stressed. Also, fungal infections do not necessarily happen as a result of of age. Age cannot be changed, but a fungal infection can be cured.

Click to expand...

Sadly she ended up being put down she didn’t get better with salt or a anti fungal treatment.

FranciscoB said:

It is a fungus but I would not describe it as fin fungus. In fact, it is in the caudal peduncle, and extends outwards including part of the caudal fin. Very likely started upon a wound in the body (even if small), and grew from there. At this time it s quite extensive but it should be stoppable.
The suggestion of salt + maintaining the absolutely best water quality possible is the the way to go and should result in improvement.

Click to expand...

Sadly she ended up being put down she didn’t get better with salt or an anti fungal treatment. Still don’t know what happened.

Saprolgenia Fungus can only get into an open wound so the fish must have scratched itself and that allowed the fungus to gain entry.

Colin_T said:

Saprolgenia Fungus can only get into an open wound so the fish must have scratched itself and that allowed the fungus to gain entry.

Click to expand...

Can other fish get it? I have 4 betta girls in that tank. Do they have to get a scratch to get it or can it spread now that it’s in the tank?

Thebobcats said:

Can other fish get it? I have 4 betta girls in that tank. Do they have to get a scratch to get it or can it spread now that it’s in the tank?

Click to expand...

Mind then that the original wound that lead to this was probably betta-to-betta aggression.
Sororities are trendy but tricky.

Thebobcats said:

Can other fish get it? I have 4 betta girls in that tank. Do they have to get a scratch to get it or can it spread now that it’s in the tank?

Click to expand...

The fungus can only gain entry via an open wound. If the fish don't get injured, they won't get the fungus, which is in every aquarium and water body around the world.

Keeping the tank clean (regular water changes and gravel cleaning, cleaning the filter once a month), feeding a varied diet, and reducing aggression will prevent this from occurring.