Lethargic Betta help

It is a very long video (muted).

I picked up this male koi at my LFS last Friday. I’ve been setting up a planted tank specifically for a betta since late August.

The first day he was active and ate one of my shrimp. Since Saturday night he basically just lays on the floor and his breathing seems labored. He swims to the surface to breathe and then is right back down.

Information: I cycled by putting straight up ammonia in the aquarium, then used filtered media from an established fish tank (not mine, purchased), along with a biological booster.

I don’t feel my tank was fully ready, but it was extremely close. The ammonia had disappeared by mid August and my nitrites were off the charts. But then they kept declining and I didn’t really get a ton of nitrates… it’s hovered around that light orange now for 2-3 weeks.

That said, my shrimp are doing well, snails too. This was a fish in a cup and what I have seemed much better than that.

Now I’ve been stressed about my poor stressed fish that I thought I’d made the perfect home for and I really need help.

— This video is morning light. My tank gets 6ish hours of a higher intensity for the plants. He definitely doesn’t like the bright light and will move to the shade. I left the lights fully off for 24 hours yesterday.

Parameters in a comment below with test photo. Please help!