My husband and I had 4 fish and a shrimp, we had to travel for a week and came back to 3 white decomposed bodies of fish and one, I guess, leftovers of a body... Yet, the shrimp was still alive! Now we came back and found the central AC broken and I assumed the heat killed them, but the temperature of the aquarium is 25 degrees Celsius only; tank size is 75L. We've had 2 fish for over a year and the other 2 were like a month old; also, we had an auto feeder working, so they were fed for sure.

Now, what could be the reason they all died together?


2 Answers 2


Lots of things can go wrong. Here are some ideas:

  • pH or ammonia spike : The larger the tank, the less likely spikes are, but all of my catastrophic failures like this were due to spikes

  • Power outage : If the power went out, all electrical components would stop functioning, like the heater, filter, aerator etc.

  • Feeder malfunction : Especially if you haven't tested it before, it could easily have malfunctioned, putting way too much feed or way too little.

  • Domino effect : It's important to realize that decomposing fish bodies cause all sorts of issues and unhealthiness, so a single death could have caused a cascading effect

  • 1
    I think this would not be a problem for fish if they did not eat for a week - especially, if the scenario is that they killed one and ate it. I would expect there was power outage and they died because of low oxygen, restarted filtering etc.
    – Voitcus
    Commented Jul 7, 2015 at 4:15

Addition to rib.usa's answer.

I think that typical fish could survive a week without eating.

Probably there was a power outage, which stopped all electric devices from operating. The time was long enough all the bacteria in the filter died and the filter became a source of poisonous substances. If the power was reconnected automatically by your utility, all these substances have been injected to the tank causing fish to die. Salt-water fish are much more susceptible to bad conditions than fresh water ones.

If there was "central AC broken", which I understand as there was a short-circuit in your tank. Perhaps the heater is down - maybe current flow killed the fish. I had such an event twice, however, all fish survived and did not even noticed.

What is also possible that there was a disease. Maybe some insect dropped to the tank and was eaten.

Unfortunately, if this was nothing with the equipment, you might never learn what had happened.

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