Fin/body rot what to do

My betta a couple weeks ago just completely ripped off his dorsal fin. Theres nothing in the tank that he could have ripped it on, no tank mates (other than a snail), he has been known to bite his own fins and i cant make him stop.
He was getting better by not giving himself haircuts and his fins were staring to grow back to their full length but then he bit off his entire dorsal fin. For a couple days it seemed to be healing itself so i didn’t interfere. Ive been busy and havent gotten to look at him. I looked closely at him today and it has turned white, along with parts of his upper body.
I dont know what i should do? To a 50% water change then dose the tank with medicine? Give him a salt bath?

He is still swimming fine, not flashing or acting hurt. Along with eating okay. The last picture is my most recent picture before he did this entirely, when he still had most of his dorsal fin intact.

My betta a couple weeks ago just completely ripped off his dorsal fin. Theres nothing in the tank that he could have ripped it on, no tank mates (other than a snail), he has been known to bite his own fins and i cant make him stop.
He was getting better by not giving himself haircuts and his fins were staring to grow back to their full length but then he bit off his entire dorsal fin. For a couple days it seemed to be healing itself so i didn’t interfere. Ive been busy and havent gotten to look at him. I looked closely at him today and it has turned white, along with parts of his upper body.
I dont know what i should do? To a 50% water change then dose the tank with medicine? Give him a salt bath?

He is still swimming fine, not flashing or acting hurt. Along with eating okay. The last picture is my most recent picture before he did this entirely, when he still had most of his dorsal fin intact.

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I am so sorry that your Betta Splendens is biting its own tail. He is still beautiful. I've not dealt with this issue before but I did some searching. Maybe these two threads may help you to start finding the solution. Remember you are not going through this alone:

https://www.fishlore.com/aquariumfishforum/resources/tips-for-a-tail-biting-betta.256/

and this reply here looks good:

I am sure someone more knowledgeable will reply soon! Keep us updated.

I have come to believe that fin biting is a stereotypical behavioural response to stress the fish cannot manage any other way, which is why the behaviour usually won’t stop no matter what you do to try and help.

At best it can be managed. At worst, the fish has a shorter (maybe a much shorter) lifespan because severe stress can kill.

Self destructive behaviours due to stress are very common in multiple species when they’re kept in captivity and it affects humans and livestock as well as zoo specimens. V

Enrichment is what zoos practice to try to alleviate the stress so as to prevent stereotypical behaviours from starting.

Unfortunately, we don’t know precisely what stress or stresses are the problem for any given fish, so it can be challenging to identify what changes might need to be made.

I suspect there could be a genetic component involved as well, though I can offer no proof that this is so - it’s just something I suspect and if it’s true there’s nothing we could do about it except refrain from breeding any fish that bites its fins.

That bitten dorsal is a serious issue because it’s so close to the body wall. I would want to paint that entire dorsal area with full strength methylene blue.

However, where I’m sure stress is already a problem, I’m rather hesitant to catch up the fish in a net to apply it, because that too is stressful. Being caught is stressful no matter how we do it, but there are gentler methods than using a net.

If you could very gently scoop him into a cup or glass without chasing him around, that should be less stressful.

Then let the water slide out while making sure the fish doesn’t go with it, until the topline of the fish is exposed to the air.

Then, as quick as quick can be, pour liberal amounts of MB over the dorsal area. Dip the edge of the container to add a little more water to help rinse off the excess. Pour off as much of that as you can and then submerge the container and let him swim out. Not a stress free experience but hopefully one that’s less distressing than being chased with a net.

MB is a powerful disinfectant with excellent antifungal and antibacterial properties. Additionally, it will stain any tissue on a fish that has a broken or missing slime coat blue. That is useful.

Mind, the staining can only tell us there’s no slime coat. But lack of a slime coat means there’s a very high chance there is an infection present.

So if the MB stains the area, you can be reasonably sure there is an infection and if not, there isn’t. Either way you learn something useful.

If it stains, you can either repeat the MB application daily for a few days, or decide to use an antibiotic if you have access to them.

Mix the antibiotic with food because the risk of an infection penetrating into the body and bloodstream from a fin that’s been bitten this short is extremely high.

Adding an antibiotic to the water doesn’t work well for any problem within the body. It needs to be ingested or injected to have a shot at doing its job. If you choose to use antibiotics, do it asap and choose something broad spectrum and use MB in the interim.