Someone PLEASE tell me what the hell happened!!!! I did a water change 3 days ago & levels were good. Woke up this morning to almost all my fish dead & others in process. After freaking, checked levels & they are PERFECT!!! I don’t know what I did??? Why would this be? I don’t know what in the world to do???? Water very clear! Please tell me what to do!!! Also, none of fish have shown any signs of illness & were doing great!