How to Cope with Different Kinds of Aquarium Crisis

Even the most careful aquarist may suddenly be faced with a crisis. You can protect the fish to a degree by trying to anticipate possible problems and by knowing how to respond appropriately and promptly if something goes wrong. Sensible precautions might including having a spare heaterstat available, in case the one in the tank fails when it is impossible to obtain a replacement quickly.


Certain household chemicals that might seem inoffensive can actually prove deadly if they are drawn into the aquarium through the air pump. Aerosol products, such as those used to kill fleas on dogs and cats are especially dangerous for this reason, as are other insecticidal sprays, such as fly and bug killers. Try to avoid using such products in the home, certainly in the same room as the fish.

The specific signs will vary depending upon the chemicals concerned, but a sudden wipe-out of an apparently healthy aquarium of fish would strongly suggest poisoning as the cause of death. If you do discover dead and dying fish in the aquarium, you should obviously remove any fish that are still alive to a container of dechlorinated water immediately, in the hope that they will recover.

Tracing the source of the poison can prove to be difficult in some cases, but you should be suspicious of the water itself if symptoms develop soon after a partial water change. Perhaps you have forgotten to add the water conditioner, leaving the fish exposed to a potentially high level of chlorine or chloramine. Adding this without delay may well resolve the situation before there are any further fatalities.

Pesticides in tap water

Another possibility, if you notice signs of poisoning after a water change, is that the problem stems from pesticides in the tap water. Pyrethrins, or their artificial counterparts which are known as permethrins, are typically added to water to flush the pipework and kill off any invertebrates that might be present. Some species of fish are considerably more susceptible than others to these pesticides. When water companies are planning to add these chemicals, they normally advise local fish-keeping groups of their intentions, but you may prefer to contact your local water supplier directly to ascertain the situation.

What to do in a power failure

When a power failure occurs, not only will the water temperature start to fall, but aeration will cease, compromizing the efficiency of a biological filter containing aerobic bacteria, and the lights will go off. The most serious long-term effects may be on the filter, but there is little you can do to safeguard its efficiency.

  • Insulate the tank – The first action you must take is to insulate the aquarium by covering it, and so minimize heat loss from the water. Use a thick blanket or even a duvet or quilt for this purpose.
  • Monitor the temperature – You can keep a check on the temperature without having to open the hood. Provided that the room itself is reasonably warm, then the temperature should only decline slowly, enabling the fish to adjust gradually with no major ill-effects if the power supply is restored without too much delay.
  • Prevent fire hazards – Never cover the air pump, or leave the lights switched on, because the restoration of power may cause the covering to catch alight, if it occurs unexpectedly at night while you are asleep.

Extended power loss

It is not a good idea to add hot water to the aquarium, even if you have an alternative source of power that enables you to heat water. The fluctuating temperatures will be more stressful for the fish, and boiling also affects the relative hardness of the water, altering the water chemistry within the aquarium. In any event, you could not add any warmer water without removing some of the existing water, and if you needed to repeat the procedure to maintain the temperature, you would exceed the recommended volume change. Floating a hot water bottle on the surface, or placing one or two around the outside, is a much safer option to provide additional warmth if the power is off for a long period.

What to do afterwards

The lack of illumination will do no harm in the short term, but once the power is restored, it is a good idea to leave the lights on for the usual amount of time. The heaterstat will then switch on again, and the water will warm up slowly, so that, as before, the fish should not be unduly stressed by the changing water temperature.

  • Check the filter – Check that the filter is working properly after being switched off; if the power has been off for long, you may want to add a beneficial culture of bacteria to seed the filter bed again.
  • Monitor water quality – Keep a close watch on the levels of ammonia and nitrite in the water after a power failure, to check that the bacterial population has not been badly damaged by the shortage of oxygen. If necessary, you will have to use zeolite sachets and activated carbon to remedy the damage in the short term until you are sure that the biological capacity of the filter is fully restored.
  • Observe the fish – The fish should recover without problems, with the water temperature rising gradually once the heater is switched on again. Watch them closely for the first week or so afterwards, however, for signs of an opportunistic fungal or bacterial infection as the result of being chilled.

Coping with a dying fish

If you ever find a fish beyond hope of recovery, it should be killed humanely and quickly to prevent further suffering. A vet can do this for you, but you may prefer not to subject your fish to the additional stress of being caught and transported to the surgery. If the fish is small, crushing it quickly with a block is probably the most humane method, but with a larger individual, cutting through the spinal cord behind the neck and decapitating it is a better option.

Never flush a dying fish down the toilet or drain. This is cruel, and could prolong its suffering considerably. Nor should sickly small fish ever be offered to larger carnivorous species, since this can spread the infection through your collection, as well as possibly giving the sick fish a protracted end. If you are unsure as to the cause of death of a number of fish, keep the bodies cool and take them for autopsy to your local veterinary surgery as soon as possible after death, along with a sample of the aquarium water plus details of their care.

Filed Under: Pets & Animals


About the Author: Fred Goodson has a passion for pets and animals. He has 4 dogs and is planning to have another one. He is also a blogger who writes about pets and animals. Currently, he is living in New Jersey.

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