Originally Posted by jeffaquarius
Do you have lots of Coraline Algae and good water circulation and water surface agitation? What were your pH and alk
readings the morning the fish were dead? Lack of oxygen is another possibility.
The typical sign of fish that die from asphyxiation (lack of oxygen) is their gills will be flared out due to trying to breathe the largest breaths causing their gills to flare. This state would be seen in all the dead fish as well. "normal" appearance is usually a sign of biological demise. ( i.e. disease, old age, etc.)
The electric issue bares looking in to. Heaters, cracked heaters actually, can leak an electrical charge into the water which may have done the fish in. It could also have been from any other electrical item in the tank. You may want to use a voltage meter to check the tank for electricity leaks before adding anything back to the tank or replacing machinery. If you do show electric in the tank, start unplugging each machine one by one to see which item is leaking the charge. It used to happen frequently with submersible power heads so I won;t jumpt to conclusion that it's from the heater.
Hope this helps