I have a 40 gallon tank. I set it up 3 weeks ago, I have 2 balloon mollies that are doing great. Last week I bought 10 neon tetras, after 3 days they all died out of nowhere. Today I bought 6 rumynose and 10 neon tetras. After 6 hours they all died again at the same time. I used to have neon tetras before and never had this problem. Can anyone tell my why this is happening and why are they all dying at the same time. This makes me never want to buy them again. I had an easier time keeping discus alive.