Yes that is fin rot.
What is your water like, ammonia, nitrite, nitrate?
What size tank is he in?
Fin rot is caused by high ammonia due to an uncycled tank. Prioritize buying an API Master Test kit and post the results!
For now, if he is in a 2.5 gallon or less change 100% of the water every day. if he isn't a 5 gallon or more, change 50% of the water every day.
Clean water is the key to healing a rotting tail.
Ok thanks. I did a water change today, he is in a 2.5 gal tank and I cleaned it really well. He is my daughters fish and I admit his tank is not cleaned weekly. But now it will be. Should I add the betafix?
It has been a week since I figured out that my betta most likely has fin rot. Have been doing daily water changes. How long am I supposed to continue this and what should I expect to be seeing in terms of recovery if there is any?