Betta Fish: Barry is being weird and idk why

My half Moon is currently in a 5 gallon tank with two sponge filters and an extra air stone. I've been convinced that something was wrong for about 2 weeks. He hangs at the bottom, rarely comes up for air, hides all the time, and only eats when the food falls to the bottom. My most recent testing and water change was last weekend. Ammonia and nitrate 0. Nitrate 15. KH 3. GH 11. pH 7.6. temperature 78°. There's one mystery snail in the tank with him. And three to four live plants. The smoothest rocks that are available and a couple pieces of smooth driftwood. I have a couple almond leaves in there now and keep them in most of the time.

At this point, when he finally sees me from wherever he's hiding, he peeks his head out. If I start watching the snail – because he's much more active than my sweet little betta fish, he comes out further. It's literally like this boy is jealous. I am completely out of ideas. I did replace the water during my last water change (about 40%), with 75% of the purified water I typically purchase and 25% RO. My tap water is too hard even though the purified water is still producing a pretty high GH. I'm trying to slightly elevate the KH without raising the GH or the pH, hoping to avoid any pH swings that could be happening throughout the day and night. If I could bring the pH down just a smidge I'd be even happier. I have two other betta fish, both in separate tanks. One of those is male and one is female and they both have nearly identical water parameters and setups and are thriving.

With the research I've done, I thought maybe there was poor oxygen so I added the extra air stone and a second sponge filter to increase surface movement. His fins are less beautiful than they used to be, I haven't seen him nipping at them directly, but it did look like maybe he did once recently when he deliberately swam right through and into one of the live plants. This plant is tiny, smaller than the fish, but the leaves were snagging on his curly, dangly fins. He turned around, attempting to get out, something I wouldn't think a healthy fish would really struggle to do with such a tiny plant that gets uprooted consistently by my snail. While I couldn't tell if he was nipping or just trying to free himself, there is a chance that he is doing some fin nipping. Sometimes I play tic-tac-toe with him on the glass and he has come to the glass and been very interested. He's not disinterested in interacting or engaging with me but his whole demeanor has changed in the last 2 weeks.

If anyone on this thread has any suggestions, I'm open to it. I'm also open to learning more about what might be going on with him. I'm starting to resign myself to the idea that maybe he's just a fish that likes to be hidden and chill. He's very young, was obviously a juvenile when I got him. He is probably 1-year-old now.

First 2 pics are of him when I got him in August.

Third and fourth are from early March.

Last pic is today.