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Adding Essential Oils To Fish Tanks ( The Pros & Cons )


If the question is, is it OK to begin adding essential oils to fish tanks? Then the answer is YES.

But if the question is, should you add essential oils to fish tanks? Then the answer is NO, as there are too many variables to consider, and the dangers far outweigh any potential benefits.

However, not all fishkeepers will agree with that statement. And that is where the confusion begins for many people.

So let’s take a closer look at essential oils, what they are, and what they do; plus how to deliver them safely.

Finally, I will end with the pros and cons of adding essential oils to fish tanks discovering which oils are safe and which are toxic. 

Adding Essential Oils To Fish Tanks

What Are Essential Oils?

Essential oils are multicomponent volatile liquids of a lipophilic nature contained within the leaves, flowers, bark, seeds, and the rinds of many plants.

Each essential oil can have up to 200 individual components comprising of thousands of different chemicals.

Furthermore, each oil is unique as it is a natural extract and varying environmental conditions influence its growth and development.  

Each essential oil should have a Material Safety Data Sheet (MSDS) that provides toxicity information, flammability warnings, and disposal directions.

Interestingly, according to their MSDS sheets, many oils are toxic to aquatic life and can have long-lasting impacts on marine ecosystems. 

Basically, every essential oil is a complex mix of chemicals, and you should not think of them as simple liquids.

Therefore, adding essential oils to your fish tank will produce a distinct change to the water composition—a change where your delicately balanced aquatic environment may not react positively.

Why Add Essential Oil To A Fish Tank?  


Many fish tank holding households already use essential oils in aromatic diffusers and practice holistic medicine at home.

So why not extend the medicinal qualities of essential oils to the fish tank, especially as essential oils are seen as an organic and a safe way to treat many ailments.

This openness to experiment, combined with the belief that it is a safe product, has resulted in new information online regarding fish care.

Here fish enthusiasts experimenting with essential oils report that they believe they have found a new way to improve the lives of the fish.

Using essential oils, they believe that they can organically combat bacterial growth, viruses, fungus, and other adverse health concerns.

Claims of Success have been reported using weekly treatments of Lemon, Peppermint, Purification, or Clove oils, but claims of success are limited.

I also find the reporting of Lemon and Peppermint as choices perplexing as these are typically oils that can cause internal and external irritation.

In addition to this, all reporting is positive but lacks the detail and consistency of scientific study.

However, I find that negative results are seldom published, so please be objective when reading them.

Fish And Essential Oils (The Scientific Research)

Most scientific and measurable research that essential oils are good for fish comes from the fish farming industry.

Both freshwater and seawater fish have been monitored, and the results documented. 

Unfortunately, the research is limited regarding the number of fish species and focuses mainly on combating parasital growth, stress from fish transportation, and feed benefits. (Source)

However, the research results show promise in all three areas; although, they are not consistent across all of the fish species tested. (Source)

Nor was it possible to find an essential oil that remained consistent in chemical make up over long periods.

Consistency being hard to achieve with an organic product due to the many variables related to each crop.

Plant variables such as chemotype, climate, soil type, PH level, essential oil extraction point, handling, and distillation methods all contribute to altering the composition of each essential oil. 

This uncontrolled variance is a significant factor in results analysis and the subsequent reporting of effects. 

Furthermore, it was found that some species displayed a varying but measurable reaction when being tested.

However, other species undergoing the same test parameters showed no reaction at all. (Source) 

Concluding that care must be taken when selecting essential oils to treat fish outside of a specific grouping. (As would be the case in a mixed species fish tank).

Happily, the research regarding the addition of essential oils to foods targeted at a specific fish species remains positive.

Here, the delivery method, essential oil composition, and ingestion level can be tightly controlled, and the effects monitored.

How To Add Essential Oils To A Fish Tank 


The scientific evidence gathered so far informs us that different fish react differently to different essential oils.

Therefore, I would never advise a hobbyist to add essential oils to a mixed species fish tank.

I would also urge you to do your research first and start slow and low for single-species fish tanks.

Furthermore, as essential oils react with plastic, you should only add essential oils to a glass fish tank.

Avoid the addition of soft plastic components wherever possible and regularly check them for wear. 

However, frequent water changes and oil decomposition through heat, light, and humidity will significantly mitigate the detrimental effects. 

Those wishing to add essential oil to a fish tank should only do it with a toothpick dipped into the oil and then into the water.

The toothpick should not be allowed to drift and be removed from the water once the oil has stopped seeping. 

Following this, it would be best to observe the fish over a long period before adding more oil.

Some fishkeeping sites have suggested that you can slowly build up the oil concentration to approximately 2 – 5 drops per 10 gallons of water.

The liquid should be premixed in a sterile container and then slowly added to the fish tank. (Source)

However, I find this advice highly suspect and would question the evidence for this statement.

Is the evidence scientific, anecdotal, from personal experience, or just coming from someone who has an interest in selling you essential oils?

But no matter what, my advice is never to add droplets of essential oil onto the surface of the water.

Plant extracts of this concentration do not appear naturally in nature and will kill any fish that ingests it.

Indications Of Essential Oil Poisoning In Fish

  • Gasping at the surface
  • Flicking or trying to jump out of the water
  • Enhanced coloring
  • Gasping near the bottom or at a favorite spot
  • Erratic behavior and fast changes in speed
  • Spotting or dark marks appearing on the body
  • Lethargic behavior

If you spot these conditions in your fish after introducing essential oils to your fish tank, you must immediately complete a 20% water change.

Increase this up to a maximum of 50% if no significant change is forthcoming.

However, do not be tempted to go above this, as the sudden environmental change will stress the fish.

Never be tempted to introduce a new oil to counteract the oil that has caused the problem.

Remember, the solution to your pollution lies only in dilution.

The Dangers Of Experimenting With Essential Oils In A Fish Tank


The scientific evidence shows that not all species of fish exposed to essential oils will react in the same way.

What may be tolerable for one species might cause extreme stress or kill another. Therefore it would be dangerous to expose mixed groups of fish to essential oils.

Another point to be made here is that fish tanks support varying life forms within the delicately balanced aquatic environment. 

Plants, healthy bacteria, coral, shrimp, etc., can all be adversely affected by the addition of a foreign chemical.

In regards to fish, size, health, sex, age, and pregnancy can also be important determining factors. 

And remember, you have no idea what these oils contain as the essential oil industry is self-regulated. 

One bad oil can decimate the aquatic environment making it unrecoverable.

And even a genuine oil given at the wrong concentration or duration of exposure will have the same devasting effects. 

Essential Oil And Fish Tank Water Do Not Mix

Essential oils are lipophilic (not water-soluble), which means that microdroplets of oil will combine and form a thin layer on the water’s surface. 

The effect will be a reduction in the transfer of oxygen into the water and increasingly stressed fish.

Another consequence will be oil ingestion, which can also trigger a stress reaction or worse.

Furthermore, a well-maintained fish tank has a water pump and filtration system, which will draw the oil in and trap it.

However, this will interfere with and may destroy the carefully managed bacterial system that resides here.

Once this system is gone, the fish will suffer as their immune systems weaken, opening them to vulnerabilities. 

Oil in the water could also damage the gills making breathing difficult or damaging the mucus coating the fish’s skin.

Mucus is vitally important to a fish as it holds antimicrobial peptides and enzymes that actively attack dangerous pathogens.

Without this protective layer, fish are particularly vulnerable to attack, even from other fish. (Source)

It is also possible that microdroplets of oil will begin to coat the surface of any plants present, reducing their ability to survive.

In addition, rotting plant life decreases oxygen production and places more bacteria into the water. 

Diffusing Essential Oils Near A Fish Tank


Warming essential oil in a diffuser will alter the oil’s chemical composition and the predicted effect.

Therefore I only recommend cold air diffusers in homes with pets where diffusing will take place.

To minimize the risk to fish, diffusing essential oils should only be done in a room not containing a fish tank.

In addition, any diffusing should only be for short periods, and you should never diffuse any Petroleum-based synthetic oils. 

Throughout diffusing, all life within the fish tank should be observed for stress-related symptoms or behavioral changes.

Additionally, the fish water, plants, gravel, and structural features should be periodically checked for signs of oil build-up. 

Which Essential Oils Are Safe For Fish?

In my opinion, there are too many species of fish to accurately produce a safe list of oils that will encompass all fish.

However, the research shows that fish can prosper from specific essential oils within tight tolerance levels. 

Unfortunately, the parameters are so tight and the variations so huge that the risks begin to outweigh the gains.

For example, Clove is widely used in the fish transportation industry as an anesthetic to mitigate stress.

However, a common observation is that the substance itself may pose a stress trigger. 

Here lies proof that even this highly used oil can quickly turn from the cure to the poison.

Furthermore, the fish transportation industry uses essential oils as active sources of control against fish parasites.

But although more than 3000 Essential oils are known, less than 0.4% of them have to date been tested on fish parasites. (Source) 

This is why essential oils added to commercial food and medicines is the only safe route to choose when adding essential oils to a fish tank. 

Personally, I would never recommend adding any essential oils into a fish tank by any other method.

Commercial products should not be used as a guide to determine a safe for fish essentials oils list.

The oils contained within them are highly diluted and tested for chemical quality and consistency within a targeted delivery system.

Do not make the mistake of thinking that your local essential oils are a good safe and cheaper substitute.

Moreover, the experimentation of essential oils within small fish tanks should only be carried out by those qualified in fish welfare.

Essential Oils Toxic To Fish

The oils posing the most significant risk to fish from accidental contamination are those high in phenols, ketones, d-limonene, and the monoterpene called alpha-pinene. 

This list represents the most popular essential oils used around the home that fish find most reactive.

It should not be seen as a totally comprehensive list of all essential oils harmful to fish. 

essential oils toxic to fish

Once again, I must stress that not all fishkeepers will agree with this article’s contents or the list of toxic oils. Some will be even be using some of the oils to treat their fish.

However, I believe the risks are too high.

Essential oils are highly concentrated volatile compounds in an unregulated industry, providing unknown and untested chemicals for human use.

We cannot humanize fish and treat them with these oils as we would a human. 

Not All Essential Oils Are The Same.

essential oil dangerous to fish

A true, and 100% pure essential oil, is a complex mix of aromatic substances and compounds derived from plants. 

However, the essential oil market is enormous, and adulteration with cheaper synthetics and additives is hardly unknown.

So how can you be confident that your essential oil is an actual botanical extract?

Furthermore, not all essential oils are of the same purity, third-party tested, 100% organic, or pesticide-free, which means that when you place an essential oil into your fish tank, you could be adding poison to the water. 

If you plan to add essential oils to your fish tank, please do your research first and find a reputable supplier.

Essential oil companies spend a lot of time, money, and research to supply you with a quality product. So if it’s cheap, it ain’t genuine! 

Reputable Third-Party Tested Essential Oil Suppliers

health-essential oils for fish

Do not look upon this list as being full, complete, or trustworthy. Like any list, it is only as good as the day I compiled it; therefore, things may have changed.

  • Plant Therapy
  • Eden’s Garden
  • Revive
  • doTERRA
  • Original Swiss Aromatics
  • Rocky Mountain Oils
  • Young Living
  • Aura Cacia
  • Lisse Essentials
  • Mountain Rose Herbs
  • Now Foods Essential Oils

However, with good tank maintenance, there’s really no need to use additives that are risky, unproven, and potentially harmful to the fish.

In Conclusion

Personally, I would advise anyone reading this NOT to begin adding essential oils to fish tanks of mixed-species.

And I would like to see scientific testing results derived from a home aquarium setup. 

Remember, there are over 3,000 known essential oils, and the research here is incredibly small.

Please be safe with your fish, and please do not add foreign untested inconsistent additives of questionable quality to fish tanks.


A proud father of two boys, an amateur actor, and a green living enthusiast, Mark has been sharing hints, tips, and sustainable living content on his website Sustainability Dad since august 2019.

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