Hi again, everyone!
So, I bought a new betta today. He looked a little stressed in his cup, but not terrible. His cup was cracked and water was leaking from it slightly, so I wonder if someone dropped him, hence the excess apparent stress. I brought him home and acclimated him over a few hours before releasing him into a 2.5 gallon, heated tank. He's not looking so great tonight, though. He's just kind of resting on the bottom. The tank has been treated with Prime and nothing else. I noticed that the temp had climbed to 82*, so it's lowering again. Otherwise, there doesn't seem to be anything else wrong with the setup. He also ate a few NLS pellets earlier.
Anyone have any advice? I don't know if I should just shut out the lights and cover the tank with a blanket so he can rest overnight and maybe feel better in the morning? I'm afraid of just leaving it alone, though, and having him be dead in the morning. He also seems to be a tail biter, based on what I can see of his fins. I can try to get a picture here, but the lighting in my apartment is not good at night. He's not actually laying on his side on the bottom, just resting down there. No other signs of illness that I've noticed. Thanks for any tips you have to offer!