1) Heater (Optional)
Is not necessary if you live in a tropical countries.
(I am living in Malaysia and the water temperature is around 25°-28°). If you live in a countries with four seasons, you will be needed a heater.
2) Air pump (Optional)
Is not necessary to have an air pump. Betta fish can survive without an air pump because they have a special respiratory organ called a labyrinth. Therefore, they just need very small amounts of oxygen. If you are keeping betta fish with other types of fish, then you will be needed an air pump.
3) Aquarium filter (Optional)
I don’t install a filter because I do changes the water regularly. (Twice a week, 50% of the water every time). If you install a filter, please make sure the water flow is not too strong because they like calmer waters.
Acclimate your fish before placing it into the tank.
Bad water condition, stress or hungry will lead to Betta fish jump out from the tank.
Healthy Fish: Swimming around.
Unhealthy Fish: Sinking at the bottom or hiding always.