Betta water temperature

[mutt]

I have one male crowntail betta in an aquarium shaped like a lava lamp. It was one of those "all in one" kits with the tank, stones, and air stone/pump. He seems ok but I read that bettas actually prefer warmer water. As this tank didn't come with a heater, like most betta tanks, any suggestions how to warm it? A traditional over the back heater isn't going to work, and I have cats so it's mandatory the lid stay on top. This is the actual one I bought:

http://www.petsmart.com/global/produ...N=2037042&Ne=2

Since the top is solid, a top heater isn't going to work very well either. So I'm stuck on ideas.

Like I said, he does seem fine. He eats, he swims, he puffs up, he has nice color, etc. He did have a small "bubble" between his front fins which I was advised was from too much air. Since bettas go to the surface to breathe, I removed the air stone, the bubbles went away, and he's been fine ever since.

I would like to keep this tank but I also want to provide the right water conditions for my fish. Any suggestions appreciated.

Thanks

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[Jaysn]

I've seen small flat heaters, 7.5W or so, at petsmart/co.

[mutt]

Flat heater? I looked on both of the websites and found totally submersible heaters which is great but I still would need to put the cap on the aquarium, not sure how to manage that with a cord. It would have to be some form of external heating I would suppose.

[sazzy]

i kept one of my males in a 4uk gal tank in my bedroom and didnt need a heater as they prefer it to be only slightly higher than room temp, and as my bedroom is really quite warm, he was fine and healthy until i gave him away.

[Jaysn]

I don't know of any external heaters for fish, although I have seen reptile undertank heaters. You could always take a pair of nippers to the cap, cut out a little square to pass the cord through. If you google "flat aquarium heater" there are several listed.