I just purchased three danios today. I am a beginner. My tank has not been cycled. My LFS said that I needed to cycle my tank, they said that I should start with the danios. Are two of my three danios dead because the tank wasn't cycled? If so , how do I cycle my tank and get my fish to not die? The other fish I was going to add in were : Two Black Skirt Tetras 1 Neon Orange Dwarf Crayfish Can fish die from a lack of oxygen? How do you make sure you have enough oxygen in your tank?