Betta Fish: Betta won’t eat, help please!

Hello!

I need some advice for my pet Betta. He hasn't been eating for days now. He doesn't seem to show any oher stress signs besides the lack of appetite.

So recently, I bought this Betta, and he has been with me for 7 days now. At first, he behaves similarly to other acclimating fish, shy and resting often.

He looks healthy, despite his condition in the pet store (In our area, local pet stores often keep bettas in plastic cup with minimal water just to submerge them). When I bought him from the store, he was rather pale.

1st day: Now, into my house, he was put in a small tank—for temporary use only as there was a little problem in his supposed aquarium. I didn't feed him, and waited for a day since he's new.

2nd day: The next day, his aquarium got resolved and I finally moved him to his own tank. In the same day (not same hour), I fed him 2 small pellets, he ate 1.

3rd day: However, the next morning, he won't eat. I thought, maybe because he is still adjusting. And in the afternoon, he has to be removed from the tank because of filtration malfunction. It was resolved quickly and he was returned as soon as possible.

4th day: The day after, he became more purplish and his tail is more vibrant—so I thought everything's well. But he still won't eat. So I mashed some pellets to soften it and form tiny balls, he only ate a nibble.

5th day – Today: He wasn't eating. I thought he was, because some of the mushed pellets were out of sight. I tried pellets and flakes, but nothing works, he won't eat.

Now, maybe it's the water conditions, so I did a water change today (water has been a week as well). And I decided to fast him first, since the uneaten food may just stress him out and foul the water.

I bought some decapsulated baby brine shrimps online and will be delivered tomorrow, and hopefully that will activate his appetite.

His behavior is well, no clamped fins, no gasping, and no fin rot or other symptoms. He likes to rest, that's true, but it doesn't seem lethargic as he still swims from time to time. As per the water parameter, its in the same conditions as my other tank with guppies and bronze corydoras—and the 2 species are doing excellent.

He's sold as a Half-Moon Betta, but I think he's actually a Super Delta. I named him Sunset because of his colors. His a real beauty, indeed. So I do not want to lose him right away.

If you know what to do, I'll gladly appreciate it. Thank you for your time reading this. ☺️