I just got a tropical fish tank a few months ago. It has different gouramis, bettas, guppies, a pleco, and some aquatic frogs in it. This morning one guppy and one gourami were dead, neither had any obvious symptoms of disease. All chemical levels in the tank appear normal. One of my female bettas i found nose down in the gravel at the back of the tank, barely breathing and her fins and all shirvelled, and the back half of her body is covered in gray film. I do not believe it is ich. Her tail is also chewed very badly. She probably won't make it, i have separated her anyway. What about the rest of my fish? are they in danger? what should I do? Could it be bacteria, or the result of bullying by other fish?