Thanks for all your replies. This is a really great site. I wasn't expecting that many and that quick to get replies. There's a lot of cool people here. I'll definitely consider getting a bigger tank, a heater, and a filter. But yea, I put Castle in a warmer spot. It's about 76˚ on where he is. He is happily swimming now and opening his fins. He also follows my finger when I run it across his tank. I started feeding him 4 Aqueon Betta pellets, too. Here's a couple of his pics:
Oh BTW, what are your guys'/gals' thoughts on brine shrimp as treats? Are they good? If so, how much of it could be fed?