Betta banging its head on the glass

Question
How can i stop my male Betta from banging its head on the glass ? It doesn't actually bangs its head but it continuously swims vigorously towards the glass. It really worries me. My Betta's tail is like 'dissolving' in the water. The tail seems torn but the fins are fine. The tip of the tail also has whitish edges. i'm from Indonesia and its a warm tropical country. Do i need a water heater for my Betta ?

Answer
It sounds like he is suffering from fin rot. Add some aquarium salt to his water at the ratio of 1 teaspoon per gallon of water. I am thinking that the water perimeters are off and that is why he has fin rot. This is almost completely preventable by doing weekly water changes by removing 25% of the water replacing it with clean conditioned water. As long as his water does not drop below 80 degrees then he should be ok. If, at any time, such as during the night, the temp drops below 80 degrees, then yes, he needs a heater. As for the swimming behavior, it is likely that he can see his reflection in the glass. If he has a tank light, only have it on for 6 to 8 hours a day. Other than that, there is not much you can do to stop this behavior. Let me know how he is doing a few days after adding the aquarium salt.