Fwiw, rot most often sets in when people forget to change the water often enough when they keep Bettas in smaller tanks or bowls. It isn't often ideal, but they can live in smaller containers if the water is kept pristine. I know a woman who's had several of her Bettas live 5-6 years, which is pretty amazing. One live to be 7 years, all in gallon bowls. But she is fanatical about the water changes. She imports young fish from Thailand. More cost, but better quality fish and some fantastic colours.
Clean water and good food are the best ways to maintain Betta fish in best condition. If you can get frozen or live food for him, he will love it. Frozen blood worms, frozen brine shrimp and live black worms and brine shrimp, are all usually relished by Bettas. You can chop or break too large frozen cubes into pieces, feed just the piece and pop the rest back in the freezer in an air tight bag.
I have one guy I call Mr. Picky, as he often refuses to eat. I got him live fruit flies and he wasn't too thrilled, but he likes fly larvae, so he gets some of those. Mr. Picky is a Polka Dot HM, with brilliant reds and deep orange spots and dashes on clear orangish fins, creamsicle colour body. Very pretty boy.
Mine are all adopted, originally all were imported from specialist breeders in Thailand. The other two will eat pellets, but not Mr. Picky. He would rather starve most days than eat pellets. All 3 of them had recovered from fin rot before I took them on. Mr. Picky had it the worst of all, so it's been nice to see his fins are growing back.
Another of my 3 adoptees, Rags, is a Green Dragon double tail HM, the third is also a Dragon, HM, blue with mustard gas, though his mustard gas yellow fins are really creamy orange, with black ruffled edges, so he's called Ruffles. He had some splits, and while I think they are healing, he so rarely flares his fins it's hard to tell. Still a handsome boy, with one of the longest ventral fins and gill fins I've ever seen.
Now Mr. Picky gets live black worms, live brine shrimp when I can source them, and whatever other live tidbits I can come up with, and some frozen things, mainly bloodworms. Btw, they are adult brine shrimp, not babies, though you could feed those too, probably. But they often do better with some live, or at least frozen foods in their diet. His friends get some of the goodies too of course.
I always have Almond Leaves in their tanks, which I remove and replace when they get to be nothing but veins and fibres. Then I toss the remains into a tank where I am trying to hatch Daisy Rice fish.
My Betta boys have live plants too. They seem to enjoy sleeping on plants that float near the surface. Rooting stems of Hygro Difformis have served, as have balls of java moss and even an Anubias leaf. I wrap trimmed pieces of plant weights around some of the stems so they'll stay more or less upright, and trim off the tops when they hit the top, and let those float to root. The boys seem to like the set up, at least, nobody has tried to leave.
Just fyi, Betta fish have been known to jump. So having a cover of some kind is a good idea. Need not be glass. Mesh or net works, just in case he decides to try jumping for joy, it prevents an unfortunate outcome.
Enjoy him.
