Right...I'm going to have to break the cycle of compliments on this setup. While it may seem visually appealing, it is torture to the fish. No fish should be kept in a bowl, no matter how big. You could maybe get away with shrimp or snails in a "tank" like this, but not fish. Before I get hit with a wave of angry responses from bowl enthousiasts, let me elaborate:
1. The shape of the bowl minimizes the surface-to-air ratio, which means that less oxygen can dissolve in the water compared to a standard rectangular/square tank. You may say that bettas breathe atmospheric air - true, but that is more of a survival mechanism in low-oxygen environments than a life-long adaptation, and may be stressful in the long run. Plus, at night the betta might want to sleep comfortably instead of having to come up for air every 2 minutes.
2. Fitting a heater in a bowl borders on the impossible, which means that the temperature in the tank can't be properly regulated. This can result in temperature fluctuations that could be dangerous to the fish.
3. Most of the time, a filter is almost impossible to install in a bowl, and an unfiltered tank poses risks of ammonia spikes (which causes significant stress to the fish and might be lethal), among others. Keeping water parametres stable in an unfiltered tank is very difficult. Not to mention that unfiltered set ups are much harder to keep clean. Going filterless could work in a large and very heavily planted tank, though.
4. The curved sides of the bowl magnify and distort everything the fish sees, which causes chronic stress. Constantly swimming around in circles is additionally damaging to the animals' spine, muscles and labyrinth organ.
So, to sum it up - your bowl (because it can't be called an aquarium) may be nice to look at, but in all other respects, it's wrong. Try swapping it even for a small 5gal rectangular tank. The visual appeal will not be lost, and both you and your fish will be happier.
My little toddler Grandson's (not exactly mine) newer Betta is doing alright didn't want to eat at first but now is like an eating machine once he got used to the food selection.
