Who Gives A Fish Forums

What's your water movement like at the surface? If it's too choppy, it might be creating inconsistent flow lower down. I'd aim for 10-15x turnover rate for torches, but with a softer delivery.

I've had instances where fish develop fin rot on a single fin, like the tail, and it doesn't affect the others. In my experience, this usually clears up quickly, and I've even seen it regrow overnight in some cases.

I think it was probably just stress from the water change, that's my guess. For the fins though, I'm still thinking it could've been from the petstore, or maybe one of the decorations in his tank. Like I said before, I'd definitely recommend switching to live plants, they're way gentler on betta fins.

Could be an ammonia spike, possibly. Don't know for sure, but in a small tank like that, it should cycle pretty quickly.

Welcome to the forum. I'm thinking it might be fin rot, would you be able to get a better picture of his fins? If it is fin rot, it's probably from PetSmart - they don't always take the best care of their bettas. Your guy is a beautiful fish, though. The sharp-edged plants in his tank could also be ...