Question about my fish tank, bubbles on surface of water??? read carefully please :)?

I'm sorry...I don't know how to treat fin rot, and I don't know how to treat a dying fish. But, I would say that if you wanted another guppy, you should probably put the Betta in a separate bowl, so that your guppies will be able to live in peace. Bettas ARE lovely fish, and your Betta would probably look fine in a tank by itself.