Sudden Death of Single Individuals

You should expect a certain attrition rate in your fish room. Fish like people often die suddenly without warning. I examine the tank carefully to see if the other fish are showing signs of stress, hanging in a group at the back of the tank or showing a loss of appetite. If the other fish are active, I assume that the dead fish was an anomaly. Even so I am wary. I will often take it as a sign that I have been overfeeding my fish. I back off heavy feeding. See the Ammonia and Other Poisons articles for further diagnosis.