We have a betta, Charmet Dan Anderson, who has been with us for about a year. He's been great. Over the past couple of weeks, I've noticed he appears to be getting smaller. Noticeably smaller -- his entire body. And over the past couple days, he's stayed at the bottom of the small aquarium, barely eating, barely swimming. He's sick, clearly. I sent a friend to Petsmart just now for aquarium salt and bettafix (recommended by woman I spoke with on the phone but now I'm reconsidering after reading reviews on that). Doesn't appear to be fin rot, though. I've looked. He's just... tiny.
I don't know exactly what to do immediately. I did change his water, 100%. I acclimated him slowly back in. He has a small tank, which I'm now learning is less than ideal (probably fits about five cups of water, along with rocks and fake plant), no filtration, and no heater. After reading here, I realize that that's not good. We'll change that.
But immediately, to help him, what are the initial steps I should take? Please help if you can; my six-year old is waiting and watching and worried, as am I. Thanks in advance for your insight.