I posted a thread earlier. I got some reponses but it seems like adding unquarantined fish to my tank has killed all of my neon tetras. I had 3 remaining and 2 of them have now died. I just did a 50% water change, and shortly during the water change the 2 died. I am worried about the rest of my fish. Is there anything else I can do? I have no idea what exactly is causing them to die.