Weird betta fish behavior?

Question
Hello Ron,
I have a red male betta fish. He lives in a 11/2-2 gallon tank with gravel and a small plant. He doesn't have a light or a filter. I change his water every week, sometimes every other week. I feed him a diet of commecial betta pellets, and freeze dried bloodworms. He also has a little mirror so that he can flare at himself whenever he wants to(I take it away, after he flares for a little while). Ever since I got him, a couple of months ago, he was just the most beautiful fish in the whole store(I got him in a fish store). He was bright red, and he always looked like he was flaring, even when he wasn't( his fins were very spread out). He shared a tank with another fish in the store, and did fine. WHen I just got him, he lived in a 1/2 gallon tank, but he seemed very unhappy, so I got a 10 gallon heated and filtered tank for him, along with a few tankmates. He was fine for a while, but then, I noticed that he was missing a part of his fin, so I moved him to a tank he is in now(11/2 gallons). HE was fine for a while, but then, a few weeks ago, I noticed that his fins were not as full, then he stopped flaring, and just stood there in a corner of his tank,I changed his water, and he got a little better, after a few days, he looks the worst I have ever seen him, he stays in the bottom most of the time, only comes up for air or to eat. I made him flare the other day, and noticed that his back fin split in two. HE doesn't want to flare anymore either, even though he will, if I hold the mirror in front of him for a long time. Even though I changed his water every week, when I touch it, it feels slimy. It's also quite cold.Could it have something to do with him being cold, or wanting a bigger tank? Another weird thing happened to him a while ago. One day I looked at him and he was all swelled up, looking more like a goldfish, than a betta. He still swam,and even flared at me when I came near the tank( he always used to do that). In the morning I woke up, and he was back to normal. Ever since that, he seemed to have a little trouble swimming, and sometimes lies on the bottom of the tank on his side. I don't know how to keep him warm, should i move him to the 10 gallon tank with the other fish? Please help!

P.S. Sorry that this was so long:)

Answer
Hi Natalya,
 It sounds like he is just getting cold. He needs a heater in his tank to keep the temperature up near about 78-80oF.  Bettas come from tropical waters and when it gets cold, they really slow down.  

-- Ron
  rcoleman@cichlidresearch.com
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