Betta Fish: I need to understand if the if is rotten or not

Hi everyone, about a week ago I got this beautiful male halfmoon, but lately I've been noticing that his tail is growing spikes. Is this normal? When I got him, he had a tiny, stringy area (probably the beginning of rot), but after putting him in my aquarium, after a few days, that tiny silky tissue fell off, leaving a hole, so I thought he was starting to grow back. I'd like an expert's opinion as soon as possible, and for now, I only have strips for tests, and the values ​​all seem normal (I got the liquid test, which should arrive this week).he eats and is very active and curious, he gets very angry with his reflection lol