I am writing this for those of us who keep our bettas in tanks or bowls that are less than 5 gallons. These could include vases, wineglasses, the little cube habitats from pet stores, etc.
I read a lot of people here telling small bowl owners "get rid of it, it's bad for your fish" but the bottom line is that some people don't have the space or the money to buy a bigger tank. Or, they spent a lot of money for a decorative setup and want to keep it.
So here are the requirements to keep a healthy betta in a small bowl. If you can't meet these requirements, then you should get a larger tank for the health of your betta.
1. Clean water.
In small bowls it's usually impossible to provide filtration and even if you do, these tanks are too small to cycle. The only way to keep the water clean is to change it - frequently. At least
50% every second day with one 100% change once or twice a week! Make sure the fresh water is treated with a water conditioner.
Another way to help water quality is to use a turkey baster to pick up any unwanted food after each feeding.
2. Heated water.
Contrary to what pet stores tell you, bettas are tropical fish and need warm water. Small tanks are vulnerable to room temperature changes; a heater prevents these. Bettas need water that is 78* F to 86*. You can get small 10 watt submersible heaters for less than $20.
This is not always possible in some tanks. In a non-cycled environment it is not as critical; it mainly adds oxygen to the water.
Some bowls and vases have little water surface exposed to air. This is a problem because it's hard for the betta to access the surface to breathe, and because there's limited gas exchange between the water and the air. To address this, get an air pump and tubing to blow some air into the tank, perhaps with an air stone. Note:
bubbles can create a strong current. You can get a valve to attach to your air hose which can control the flow of air.
A betta needs mental stimulation and places to hide. However, space is at a premium and your betta needs room to swim. You can omit gravel in the tank and just use some larger pebbles which take up less space and are easier to clean. Use a bushy silk plant with broad leaves, silk is less likely to tear fins.
Live plants are a good idea as well. They clean the water to a certain extent and are harmless to fins. I recommend a marimo moss ball. They are compact, don't root in the substrate and require minimal light and care.
Not needed and they just produce more wastes to foul the water. Even a snail produces a lot of waste. In a small bowl or tank the betta is fine by him/herself.
I hope this list will be helpful to new small-tank owners. Maybe it could be made sticky? If I have forgotten anything please feel free to add your comments.