I have kept Bettas (Siamese fighting fish) for quite some time. I don't consider myself an "expert," but I feel I am very experienced in their care and well-being. Since the environment for them is somewhat different from most tropical fish, I wanted to share my knowledge. Happy Betta Keeping!
At least a "one-half gallon" bowl or tank. Depending on the size of your "vase" and your Betta, it must have adequate water in it. A little more is even better, but they do "not" need 5 gallons of water, a heater (unless you live in the arctic) or a lot (if any) mechanical aeration. I have several in l gallon bowls, some in 2 l/2 gallon tanks with undergravel filter, rocks, plant and light and 3 in a ten gallon divided tank with undergravel filter, rocks and a plant in each section. Do not use "lead" crystal bowls or vases as the lead contained in this glass will kill a Betta. Also they have to have "air" at the top of whatever you keep them in. Do not cover a bowl (or vase) with plastic wrap, glass or a live plant in a cup unless you do have some type of mechanical aeration, as they will suffocate. They have what is called a labyrinth organ. This means that they can breathe "our" air and need this at the surface of their water in order to live. However, Bettas are "jumpers" also, and you need to be careful and cover the tops of containers with screen or netting so that he won't jump to his death on the countertop. They can survive for several hours out of the water, but I don't think any of us want that for our pet until he can be discovered.
They need clean water and a plant to "rest" on. Rocks are optional. The rocks are more for our benefit of "decorating" and hiding waste. The bowls (vases) can become somewhat bothersome as you have to change "all" the water sometimes 2 to 3 times a "week", but my feeling is if we don't want to take the time to do this when it needs it, then we shouldn't keep them. A 100 percent water change will not hurt them. As with any animal, their urine produces ammonia, and if the water is left unchanged, it will poison the fish. I also want to show them off, not make excuses for their dirty water. Make sure that you "condition" (remove chlorine and chloramine from tap water) the water with a product to do this every time you change their water. Just running water from the tap and leaving it set overnight will not permit all the "chemicals" of city water to dissipate. There are many different kinds on the market, and your LPS (local pet shop/store) can advise you as to what product they carry. They all work basically the same way. I also add 1 teaspoon of "aquarium" salt per 1 gallon of water when I do the water changes in the bowls. (This can also be purchased at LPS. They like the salt and it helps to fight disease. As closely as possible, try to make sure the water used for changing is the same temp. they were in before. The water should not be "distilled".
They need to be "fed" twice a day. I usually do this in the am and then again in the PM. If instructions came with your Betta that you don't need to feed because he will eat the roots from the plant, that is a lie. They need food, particularly protein and fat. I feed a variety, but mostly I use what is called "Betta bites." You don't need to feed but about 4 or 5 "grains" of this to be adequate, depending on his size. However, do not "overfeed." This creates waste and any leftover food fouls the water. You can fill in with frozen or dried bloodworms and frozen brine shrimp every once in a while as a treat. There is also a product called "Betta Biogold" that is very good.
Now, a very strong word of advise here. You CANNOT put two males together. They are a very territorial fish and two males will spar until one will eventually kill the other. Some do keep Bettas in a community tank, but I don't advise this practice. Because of their long, flowing fins, they catch the eye of many fish who like to nip and chase. You will find that you have one of two things. Either the Betta will become stressed and worn out from trying to run away from these fish which will rip and tear at his fins, or you will find your Betta becomes aggressive and fights with the other fish in your tank. Don't keep a male with females either. They tend to fight trying to spawn and "someone" is bound to get hurt.
There is a World-Wide craze of placing the Betta in a vase with a lily growing out of the top and the roots dangling in the water. This "decoration" is overpriced, not constructed properly and most times the instruction and care of this is not correct. If you so desire to purchase or construct a vase of this type, please adhere to the above directions for care of the fish. The main things you need to remember are: The fish has to have air at the surface; it needs to be fed protein, meat and fat and only eats the roots of the plant in order to keep from starving to death; and the water needs to be changed frequently.
Once you learn the ins and outs of Betta keeping, they are easy to keep. They originated in the "stagnant," still waters of Thailand and because of the labyrinth, they can survive in very little, dirty puddles of water. But since we are keeping them as pets, and they are so beautiful and have such neat personalities, I am sure none of us want them to be kept that way. There are many books to be found and many sites on the net concerning care of these fish. By adhering to the above instructions, you should have a happy, healthy, thriving Betta who will repay you every time you come close to him by dancing, flaring and showing you how much he appreciates the care you are giving him.