The best thing you can do for your Beta fish is to provide clean water. One of the mistakes people make is to keep their bettas in a small container or bowl and rarely or never change the beta fish water. Regular water changes will ensure your betta stays happy and healthy.
Aquarium & Fish Tank Heaters, Chillers & Thermometers | Petco
Fish, especially Betta, do not do well in bowls. Unfortunately, Betta fish are put into containers much to small for them to be happy or healthy. Many "Betta Bowls" are horrible at keeping fish. Bettas need a MINIMUM of 3 gallons (11.4 L) of water (5- 10 is ideal but the more space the better in most cases) with adjustable heating, and filtration. If you set up an aquarium that meets these requirements you will have a happy and healthy fish.
5 Affordable Betta Fish Tank Heaters You Should Know About - TFCG
Since betta fish can survive in many different types of environments, people think it's a good idea to keep them in decorative bowls or vases. In reality, bettas need plenty of space and filtered water in order to thrive. When you set up your tank, keep the health and happiness of your betta in mind. Don't forget the golden rule for bettas: never house two males in the same tank, or they'll fight to the death.
this heater is perfect for small tanks or bowls with a single Betta.
This new mini submersible heater was designed specifically for betta bowls and lets you keep your betta fish happy and healthy. The round shape allows this heater to be used in round fish bowls or rectangular tanks. Just bury it under the gravel and relax knowing the water temperature won't fluctuate enough to endanger your betta. Measures 3 1/8 inches across. Non-adjustable 7.5 wattsDon't worry about those little cups either. As long as it's a reputable pet store (one that specializes in fish, unlike Petco and Petsmart, which I tend to avoid) the water should be clean (it literally takes a couple of seconds to change the water in those cups.) But even the best of the aquarium stores keep their Betta's in those cups. Betta's do not do well in large spaces. I don't recommend keeping them in those cups when you get them home (because you need to change the water every day or two), but they are perfectly happy and healthy in a 1 gallon bowl, even a half gallon is sufficient for them as long as you make sure to keep on top of the water quality. I do not recommend using a filter on a Betta bowl however! They do not like any water circulation at all. Just do your water changes and they will thrive.