Often caused betta tail rot or betta fin rot because dirty tank. Have Bacteria in betta tank. Dirty water because overfeeding and betta poop silt under tank. Betta tank not clean or not change water take care betta fish. This is cause bacteria living betta tank and effect is betta tail rot and betta fin rot
Protect betta tail rot or betta fin rot
Keep clean betta tank change water 30% clean betta poop every 3 days and change water 100% every week. Make sure betta fish get food enough and not overfeeding.
Put betta tail rot or betta fin rot in tank water mix antibiotics oxytetracycline 1-2 gram/water 1,000 liter 3-5 days (Change water mix oxytetracycline everyday)
The best way keep clean water and betta tank always because betta tail rot and betta fin rot very hard to treatment betta fish back to normal.