If you observe that your Betta fish has problems balancing, there are several possible causes.
A common cause is Swim Bladder Disease. If you can see that his little tummy is swollen and he is having trouble staying upright or is staying at the bottom of the water tank too long, it could be swim bladder disease. This can be caused by not feeding a diet of Betta appropriate foods fed in a variety of these types of foods. For example, if you feed just one type of betta food, he may become constipated. If this goes on for too long, it could develop into swim bladder disease.
Also, swim bladder disease can be brought on by dirty tank water, and, of course, polluted water can bring on many diseases. Water in which betta fish live is so important for their health and so needs to be clean, temperature appropriate, conditioned, dechlorinated, dechloraminated, pH tested, hardness of water tested with a kit from the aquarium store, enough volume of water for each fish, not set in direct sunlight, no drafts on fish tank, and many other preparations to ensure that the water is a safe environment. See this ebook about the importance of clean water for betta fish at www.bellaonline.com/ebooks/ebook180.
To cure swim bladder disease, make more frequent and proper water changes and feed him a cooked, peeled, cooled pea. Feed in tiny little pieces small enough for a little betta fish’s mouth. This can help him pass any food that is packed in to his little digestive system if he is constipated.
Another possibility is that your betta fish has dropsy. This is a serious disease and will also cause your betta fish to have problems balancing. There are medications especially for dropsy in your local aquarium store. You can also try the old fashioned salt bath. Clean water is a must.