I had 7 glolight tetras in a ten gallon with a male betta. 2 of the tetras died. The first one I had to euthanize because he turned almost completely black and one floating at the top barely moving. The next one I found rotting in the tank
And now my betta is very lethargic and has a spot of white fuzz on his body and his tail looks very torn. His head also looks shiny. I quarantined him in a 2 gallon which is floating in the main tank to keep warm. The other tetras look very healthy. Please help me!