Unless you want to keep a Betta, I do not encourage the use of fish bowls. The reputation of a goldfish bowl is actually a baffling mystery since they are the messiest of all fish and grow too large to live in a bowl anyway. Tropical fish need better air circulation and filtration then a bowl can provide. Nevertheless, if you decide to give a fish bowl a try due to lack of budget or size constraints, heed the following advice.
Choose a bowl with a large air-to-water surface area. Avoid tall styles with narrow necks.
Use an air pump and stone. An air pump will push air through the stone, oxygenating the water and helping with circulation. This will help carbon dioxide rise to the surface to be replaced with oxygen fish needs to breathe.
Change the water once per week. With the absence of filtration, you’ll need to do your part. Replace 50% of the water. Never dump out all the water!
Use a turkey baster to siphon fish waste from the bottom during your weekly water change.
Feed every second day & be extra prudent at feeding time. Extra food rots quickly, always scoop out what is not eaten.
Keep the bowl in a place where temperature is most stable. Fluctuating water temperature can easily kill inhabitants. Avoid rooms that get cold at night or too hot when sun shines in.