Housing Bettas:
There are a number of ways in which you can keep your pet betta. Some are controversial(some ppl believe in them, some don't), some are traditional, some are non-traditional. Whichever one you choose, make sure you keep it as clean as possible. Bettas are pretty sensitive to dirty water and if you have a betta with a fragile tail (like a feather tail, halfmoon, superdelta, etc.), dirty water will fray and melt away the edges. All bettas are prone to tail and fin rot (the melting of the tail from dirty water), however some develop it sooner than others and tail type can be a factor. I will list them in no particular order, give pro's and con's of each and how to maintain this environment. I will also add my experiences with this type of environment and I won't list any here that I feel are cruel to keep bettas in. So sorry, I don't have any information on those tiny betta bowls, bettas in vases with peace lily plants on the top or similiar tanks.
1. Half Gallon jars/hexagon tanks: For a long time I was very much against keeping bettas(or any fish)in anything smaller than a 5 gallon aquarium. I have since learned that bettas really can live in tanks that are smaller than a 5 gallon aquarium, quite comfortably. A lot of breeder's keep their bettas in half-gallon jars or hex tanks, for years, and report no problems what-so-ever. Most breeder's won't go any smaller than a half-gallon, but a few in an emergency will use 1/4 gallon jars. In the past I have used 1 gallon hexagon tanks and kept a single, male betta with no problems in these tanks. Currently I am using 1/2 gallon jars, 1 gallon vases and tanks ranging from 5 gallons up to 29 gallons. Most of the hex tanks I have seen come with a filter and lighted hood(takes a nightlight bulb), but I have found the lighting is inadequate to say the least and the filter isn't a necessity but will cut your water changes in half. These tanks are large enough for a small aquarium plant, which will also help with your water changes. Setting these tanks or a jar up, is relatively easy.
Here's a tip for an inexpensive betta tank that I just read about on the internet. I read a webpage where a breeder uses glass "Sun Tea" jars, turned upside down so that the plastic lid is on top, complete with the lid as a betta tank. The lid serves as a means for keeping the betta from jumping out and b/c you keep the pour spout on the lid open, air can get in and you can feed the fish without providing a means of escape for the fish. Sometimes you can get these sun tea jars for as little as $0.88 at walmart, especially when fall first hits and all of their picnic/outdoor dishes are on sale.
Start with a clean tank/jar/hex tank. Make sure if you used soap, to rinse really well, as any residue left over can kill your fish. Take some well rinsed gravel, I usually use enough to cover the bottom of the tank, about an inch or two deep. Add that in and fill the tank up with clean water. If you live in the city and have city treated water, you will need to use something to remove the chlorine and other additives from the water. You can find a bottle of this stuff at a local petstore or online. If you have well-water, you may still want to use it, but I don't think it's necessary. Be careful with softened water though, it does contain salt (more than the recommended amount for a betta). In this case I would just use some type of bottled spring water.
After filling the tank, let it sit at least overnight so that the temperature can stabilize, before adding your fish. You should put off buying the fish until then, as well, b/c you won't have any place to put it.
As far as temperature goes, most room temperatures are just fine for bettas. However if your house drops below 70 degrees F., you may find your betta very sluggish and long term this temperature won't be healthy for him. Some breeders use clear, plastic storage containers that are shallow. These shirt-box type of containers can hold a few jars/hex's without any problems and by filling the container with water(after you put your jars/hex's in the container), you can then put a submersible aquarium heater in the water. Monitor the temp's(using a thermometer, both in the water in the container and a stick-on thermometer on each jar/hex)in the jars/hex's for a week before putting fish into the jars/hex's. Keep the temperature around 75 degrees F.-80 degrees F. I wouldn't go any higher than 82 degrees Fahrenheit and most people only use this higher temp for sick fish.
Any tank or jar without a filter, will need to have weekly water changes done. Once a week I do a 50% water change in each of my jars and then once a month I do a 100% water change. During the 100% water change, I also rinse the gravel with hot water, then with cold when it's all clean. For the jar itself, I use hot water and bleach. I make sure to rinse at least 5 times, 3 times with hot water and twice with cold water. Then I fill it up again with room temperature, bottled, spring water. Then I put the betta back in.
For lighting these types of tanks, I usually use a cheap, plant grow light ($5-$10 each at Walmart). Because all of the tanks are the same height, you can place a single grow light across a few tanks, letting it rest on the rim of the tanks. And b/c they are cheap to buy, you can buy as many as it takes to light all of your tanks. I leave my lights on my tanks all day long, turning them on around 6:00 a.m. and turning them off around 8:00 p.m.
I also thought I'd mention ways to prevent escapes with these tanks/jars. I use plastic canvas, can be found in any crafts section at the store, that I cut to fit the tops of my jars. Other people use pieces of lexan, fiberglass screening(like used on screen doors and windows)cut to size and taped to the jars/tanks, I even know some people who use pieces of paper to prevent their fish from jumping out of the tanks.
2. Larger Aquariums: By this I mean anything that is 5 gallons and larger. Set-up is basically the same as the above jars/hex tanks, the only difference is the size of the tank and larger tanks give you more decorating options...such as larger tanks allows the use of more plants(which if you use live plants will help keep your tank cleaner than no plants at all), more hiding places, etc. Larger tanks also give you the option of using an in-tank heater, a flourescent hood and less frequent water changes.
Water changes should be done once a month. I usually do a 50% water change once a month. Basically that is all a larger tank needs and if it's cycled you can get away with only doing a 20-30% once a month. Trust your water testing kit and go by that. When you see ammonia and nitrate levels rising, do a 20% water change. Wait a day and test again. Soon you will figure out how long you can go between water changes. I find it helpful to wipe the heater off with a mixture of white vinegar and water, as hard water stains can build-up on them near the water line and make them look unattractive and dirty, and I also believe that the rough texture of the hard water stains can provide a place for bacteria to grow. I wipe off the intake on the hang-on-the-back filter(which is the type I use), b/c algae, dirt and other dirty things can build-up on them as well. I use the same white vinegar and water mixture to clean the intake.
Lighting can be done in two ways. The cheap plant grow lights like I mentioned above, or with a nice, not so cheap aquarium hood. Whichever you choose, is up to you. If you do use a plant grow light, make sure to use something as a lid for the tank, to prevent your bettas from jumping out. I described a few above in the jars/hex tank section.
Temperature can be maintained quite easily, by using an intank heater and a thermometer of some type. Of course you will want to run a larger tank for at least a week without any fish in it, so that you can adjust the temperature and make sure it's stable before your fish live in it. Like I mentioned above, temp's from 75 degrees to 80 degrees Fahrenheit are best for bettas.