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  • Writer's pictureStewart Kessel

Are You Killing Your Aquarium Fish!

Updated: Jun 20

Household products and other factors that could cause you to unwittingly kill your fish

Have your fish been acting strangely? Are you suffering what seems to be unexplained fish deaths? Well, you could be unwittingly killing your fish with everyday household products.

Fishkeeping help - Are you killing your aquarium fish?

The leading cause of disease and death in aquarium fish is stress. Several factors can cause this stress. Poor water quality due to inadequate aquarium maintenance is the predominant one. However, factors such as overfeeding, a widespread issue with novice fish keepers, will also adversely affect the water quality. Maintaining the appropriate and stable water quality is the most critical consideration when ensuring the welfare of your fish. It is often said ‘fishkeeping is more to do with maintaining water quality than keeping fish’.

However, there may be some less apparent killers affecting your aquarium water quality. Numerous household products can create airborne pollutants that are toxic to your fish. For example, chemicals from aerosols and other sprays used in the room housing your aquarium can enter the aquarium water through the gas exchange process. Water is typically excellent at concentrating these materials.

Some species of fish are at an even greater risk for this type of pollutant. Labyrinth or anabantoid fish, more precisely Anabantoidei species, possess a lung-like labyrinth organ that enables them to breathe air. This group of fish include the popular Gourami, Paradise, and Betta fish. They may be subjected directly to these airborne pollutants.

Airborne Pollutants:

The list may be longer than you think. Examples include:

  • Furniture polish

  • Air fresheners

  • Scented candles

  • Insect sprays (particularly toxic to fish and worse for invertebrates)

  • Cat flea killer

  • Deodorants and perfumes (for instance, aquariums located in bedrooms)

  • Cigarette smoke

  • Paints and varnishes (for example, when decorating your room)

So, the next time you spray to freshen or clean your room or to kill those pesky flies, or light a scented candle to improve the ambience, think what effect it might have on your aquarium inhabitants. We know cigarette smoke is unhealthy for humans, so it stands to reason that it is also toxic to your aquarium inhabitants. If redecorating your room, paint or varnish fumes can be deadly to your aquarium fish and invertebrates. If possible, it is best to relocate the aquarium and or its inhabitants temporarily.

Frequent significant water changes will help keep contaminants levels low, but some pollutants like insecticides will be toxic even at unimaginably low concentrations.

Contact Pollutants:

Another consideration is contact contamination of your aquarium water. What does that mean? By way of an example, consider the following scenario: You have just finished cleaning your floor or car, and your next job is to do a water change in your aquarium. You use the same bucket to add the replacement water. Unfortunately, even the slightest trace of soap, detergent, polish, or other chemicals left in the bucket could be toxic to your fish. Thorough rinsing of the bucket might help, but the best practice is to have a dedicated set of equipment, including buckets and hoses, for your aquarium maintenance.

Similarly, we have all become accustomed to regularly washing our hands and using hand sanitiser. Undoubtedly a sensible idea after you have had your hands in the fish tank, but if doing this before, you need to ensure your hands are free from soap, perfumes and other chemicals that may be harmful to your fish.

Testing your aquarium water parameters is an integral part of maintaining a healthy aquarium. However, take care of what you do with the test reagents. However careful you think you are being, sample the water and do the tests away from the aquarium. A common mistake is to perch the test tubes on top of the aquarium whilst conducting the test. Simply knocking the test tube contents or the reagent bottle into the aquarium could have catastrophic effects.

Other less obvious household products or situations that may affect your fish

In addition to water quality, what else will stress your fish? Well, they may not have ears, but they can still detect sounds, or more specifically, sound vibrations in their environment. Therefore, an ill-placed music system, smart speaker, or television next to the aquarium could stress your fish.

Unhappy fish due to loud music

Similarly, an aquarium placed next to a door that is constantly being opened and shut could startle and stress your aquarium inhabitants, and that’s not to forget to mention those over-enthusiastic, typically young, fish enthusiasts, that tap on the glass!

To avoid noise and vibration issues, you need to carefully consider where you initially position your aquarium and what you subsequently place near it.

We don’t want to discourage those young fish keepers, so education about not tapping on the glass is the best way forward with that issue!

How to spot signs of stress and poisoning of your fish

In all cases, close observation of your fish’s behaviour and seeing anything unusual is the key to spot if something is wrong in your aquarium.

There are several ways that stress or poisoning of your fish can manifest itself.

  • Gasping for air

  • Clamped fins

  • Unusual lethargic behaviour

  • Erratic behaviour, flicking, jumping, or flashing (a fish version of scratching)

  • A marked change in body pattern or colouration*

Sudden deaths are more likely to be caused by a toxin such as a pesticide or an insecticide.

Stress and poor water quality generally inhibit the immune system of a fish, and therefore an outbreak of disease typically would indicate that conditions have been suboptimal for a while.

* The colouration of fish can change or become enhanced for several reasons, including when exhibiting breeding behaviour, but the appearance of dark bands or spots can be a sign of stress in some species.

In summary, any unusual behaviour of your aquarium inhabitants is cause for concern and needs investigating.

How to fix the problem if your fish are showing signs of poisoning

In the case of poor water quality due to pollution or lack of general maintenance, the simple answer is water changes - lots of them to dilute the offending toxins. Just be sure to condition the water before its introduction. How much and how frequent depends on the specific situation, but an immediate 50% water change and then several more over the space of a couple of days would be typical.

The temporary use of specific filter media such as activated carbon can also help remove chemical toxins. If using an external filter, you can place the chemical absorbing media in the filter media canister, in addition to completing the water changes.

Author: Stewart Kessel CChem, MRSC

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