How to Know If Aquarium Has Enough Oxygen?

An aquarium serves as an alternative abode or controlled home for fish, and it requires all essential resources to support life. These resources include water, oxygen, food supplements, etc. However, as a fish owner, you’ll want to know if your aquarium needs more oxygen or it has enough.

How to know if an aquarium has enough oxygen? Oxygen is an important resource for life, as it enhances respiration and blood flow through the body. For fish, as for humans, if oxygen is deficient in supply, then one might die or be in a very critical condition. When oxygen in the aquarium is at a low supply, fish hang at a location where filter tumbles water back into the tank or at gasp at the surface.

There are other signs that will indicate  if oxygen is not enough. You might notice fast breathing, lethargic behavior, or off-balance swimming. Hence, good oxygenation of a fish tank or aquarium is important to have a healthy-looking fish. So, let’s go over how to keep an oxygen-rich tank for healthy fish.

How to Know If Aquarium Has a Healthy Oxygen Supply?

If the aquarium has enough oxygen, fish will move about freely and look healthy – this is how to know the oxygen supply is great.

Personally, I would advise that you don’t wait till your fish start dying off before knowing the oxygen supply is limited in water. Constantly look out for signs and symptoms such as fish holding up at a particular location, water color, etc. in order to act fast.

What Causes Low Oxygen in an Aquarium?

In an effort to understand if the aquarium has enough oxygen, we need to understand what causes low oxygen in the first place. This will help you, as a reader, understand if you have a good oxygen supply or not. Here are the major causes of oxygen-deficiency in water;


This is one of the main causes of low oxygen supply in the aquarium, and this is because there are many lives competing for equal amounts of oxygen. Overcrowding could cause major fatalities, which would be an unpleasant situation for you as a pet owner, an aquarium keeper.

Putting a moderate fish quantity into the pond or tank, a moderate amount of live plants and other living organisms can help avoid overcrowding. There is nothing to worry about with oxygen levels when this is done.

The Rise in Water Temperature

Due to changes in times and seasons, there is a possibility for the water temperature to rise from cool to warm. It is important to know that warm water holds less oxygen than cooler water does. With warm water, oxygen is reduced – and this may affect the lives of organisms inside the water.

Increased heat from sunlight or heating could cause this rise in water temperature. To solve this, introduce cooler water into the tank to improve the quality of water and, ultimately, the oxygen level. In addition, ice cubes in a bag can be placed inside the water to help maintain a cool temperature.

Limited Water Movement

Another cause of oxygen deficiency is limited water movement (stagnant water). This often happens in the lower part of the tank, and in this situation, there is little or no oxygen exchange taking place. This condition makes it difficult for fish to breathe and prompts them to move to the surface to gasp for more oxygen.

Eventually, the water at the surface stops moving, too, and this means oxygen is limited in all areas. A solution to this problem is getting filters that will improve the exchange of oxygen at the surface through water movement. However, it is important to check if the current filter is working at full capacity to avoid further problems. 


Most times, why oxygen is limited in an aquarium is because of an excessive amount of waste in water, which may cause difficulty in breathing. This works side-by-side with overcrowding, and it kills much fish faster than one would expect. These wastes could be in the form of dirt, clogged filters, algae overgrowth, and fish excrement.

One good solution to this major problem is ensuring consistent cleaning of the aquarium to increase oxygen capacity. This is why it is advisable to take maintenance seriously before starting an aquarium or fish pond business because it helps. Once aquarium maintenance is considered, much the occurrence is avoided. 

Live Plants

There are some plants that cohabitate with fishes in the water. These live plants are known for giving off oxygen and taking in carbon dioxide. If these plants are available in little or no quantities, there is a reduction in the amount of oxygen that gets to these fish.

It is a symbiotic relationship where the oxygen given off by plants is useful for these fish, while the waste product dioxide given off by fish is useful as nutrients for live plants. Having more plants without overcrowding the aquarium is a very good move to ensure adequate oxygen amounts.

Chemical Concentration

In a bid to treat water and control water-borne diseases with chemicals, oxygen becomes deficient in supply. The carrying capacity reduces, and it is only a matter of time before the aquarium becomes inhabitable for fish to live. These chemicals work against oxygen in water even though the intention was to prevent diseases.

However, not all chemicals have an effect on oxygen capacity which is why one needs to be very careful with the substances used to treat water. Also, avoid consistent use of chemicals and replace them with water change to ensure a safe and healthy environment. Without chemical overload, fish will thrive, and you wouldn’t have to worry about oxygen deficiency.

What Are the Signs of Fish Dying Due to the Low Oxygen?

There are signs and symptoms that mark deficiency of oxygen in the aquarium for fishes; although, the condition is called Hypoxia, and it has its symptoms.


This is a medical condition associated with fish, whereby they suffer from oxygen deficiency in an environment. As aforementioned, this condition is caused by different factors, and if precautions are not applied, death is inevitable. With an emergency case like this, it is important to look out for signs and symptoms that are associated with hypoxia.

These symptoms include;

  • Lethargy: An abnormal behavior becomes noticeable at the outset of limited supply. Being lethargic is a common symptom of many major health conditions in both humans and animals; hence, pay close attention always.
  • Respiratory distress: Breathing becomes difficult. Fish become attracted to levels where there is little oxygen. Often times, they gasp through the surface for oxygen supply or jump out of the water.
  • Fast breathing rate: With respiratory distress, there is no doubt that breathing becomes rapid and fast. They try to inhale as much oxygen as they can in order to survive.
  • Loss of equilibrium: Swimming patterns change when the case becomes very serious. This is a very noticeable sign.

How to Avoid Oxygen Loss in an Aquarium

To improve the oxygenation of water in an aquarium for fish or avoid further oxygen loss, there are important things to do. These are ways to avoid further occurrence, and they include;

Change Water

The most important thing to do if you have your aquarium is to consistently change the water at least every week to have a safe environment.

The problem lies in the quality of water, and keeping it clean helps you get rid of water-borne diseases and oxygen deficiency. While changing the water, ensure you control the environment and make sure it is in a cool state to avoid temperature increase.

How do you keep it in a cool state? Try at least to submerge an ice-bag into the water to keep it cool all through. Cool water means healthy fish.

Add Hydrogen Peroxide

While hypoxia is a life-threatening situation, it only requires a source of oxygen to make the water habitable once again. One of the simplest ways of improving oxygen supply is adding hydrogen peroxide H2O2. What the solution does is to agitate the water surface, especially for aquarium with stagnant water.

Preparing a hydrogen peroxide solution isn’t a difficult task compared to the risk if not done. However,  there are measurements that need to be taken to prepare this solution, all of which depend on the volume of water. This needs to be done with care because fluctuation in measurements could have an effect, which will be a stress burden on the fish.

Know Oxygen Levels

There is no better way to avoid oxygen loss than testing oxygen levels on a regular basis. You may not have to do this every day, but weekly tests will go a long way. This is helpful because it gives you a heads up on what to do.

Also, you can get an electric O2 monitoring device to provide information on a daily basis. This device measures the amount of oxygen present depending on two factors, i.e., aquarium temperature and water volume. This is definitely going to save you the stress of looking for signs of hypoxia every now and then.

Get Rid of Oxygen Thieves

It is quite surprising, but there are oxygen thieves in water too. They rob these fish off required amounts of oxygen, making the aquarium inhabitable for them. These thieves are waste products and small living organisms in the water. In order to avoid this, ensure you get rid of them as soon as you can.

For instance, fish give off waste products like nitrates and ammonia that burn fish gills as well as absorb oxygen. Also, the bacteria that feed on these waste products make use of oxygen for survival too. All these added up makeup oxygen thieves in the aquarium.

Add Live Plants

Finally, make use of live plants because they have a lot to offer. Plants are good sources of oxygen to both plants and animals; oxygen exists as a waste product from plants, which is useful for everyone. So, try to introduce plant oxygen to fish in the aquarium through small live plants.

The symbiotic relationship between the two organisms is an interesting one, i.e., while the plant gives off oxygen, fish give off required CO2. However, it should be done in such a way that the habitable water won’t be overcrowded. In general, it is absolutely one of the smartest ways to avoid oxygen loss in the aquarium.  

How to Maintain a Clean Aquarium

To conclude this article on how to know if the aquarium has enough oxygen or not, let’s look at different ways to maintain a clean aquarium. These ways are effective because they have been tested and proven useful for fish in numerous ways.

Treat Algae

One other common thing that occurs in the aquarium is the infestation of algae. It occurs in small amounts until it becomes excessive in quantity, which is quite dangerous.

If algae are present in small amounts, they may not be harmful because this presence helps strike a balance in the water. However, if present in excessive quantities, algae may start feeding on live plants and the fish.

Also, it imposes a different look on the aquarium, taking away its natural beauty. Algae growth caused by three major factors: nutrients, light, and water; therefore, treating algae overgrowth comes in different dimensions depending on quantity. Manual removal works for mild growth while chemical treatment works for excessive growth.

Remove Ammonia and Nitrates

Ammonia and Nutrients are constituents of the waste product of fish that needs to be constantly removed to maintain a safe aquarium. Ammonia may not be a problem at first, but when it becomes elevated, water becomes unhealthy for fish to survive.

These elevated levels put the fish at greater risk, resulting in damage, lethargy, and then death.

In order to treat this underlying problem, once in a while, the aquarium should do something called the break-in cycle.

The Break-in Cycle

The cycle involves allowing biological colonies that convert harmful toxins to nutrients for growth to begin growing in water. These colonies grow excessively until they can convert all ammonia to usable nutrients.

However, these biological colonies are competitors of oxygen in water; hence, fish are at risk as well as live plants. Other alternatives are to make use of ammonia binder as well as filter media if ammonia levels are elevated.

Use Aquarium Salts

Salts are mostly used in freshwater aquariums for a lot of purposes. This salt present in small quantities can help reduce nitrate poisoning since nitrite elevation is inevitable at the early stage of the aquarium. Also, it can be used to improve breathing in fish as well as help in healing mild skin irritations caused as a result of substances in water.

Aquarium salts may not be too comfortable for some kinds of fish, like catfish. This is because they are scaleless, and their skin is exposed, making them vulnerable to irritations. Just in case you want to make use of salts, ensure you read about compatibility and dosing.

Use Biological Aids

It is possible to live in a healthy environment with other living organisms as long as it isn’t overcrowded. Aquarium has fish, but there are biological aids needed to strike a balance. These biological aids are colonies of beneficial bacteria and live plants; as long as colony growth is maintained, the aquarium is safe.

What these biological aids do is feed on the waste products of fish as well as other materials that can enhance their growth. However, it takes time before this balance can be achieved because regular water testing must be done at all times. Always look out for ammonia and nitrite elevation alongside.

Modify pH

pH modification is also another important thing to do in your aquarium. Most fish and living organisms in water thrive at a neutral pH; however, some prefer a lower or higher pH depending on the environment. This is the reason why pH modification is important, at least on a weekly basis.

Always test for the pH and set at the desired range. To lower pH levels, using filtered water low in mineral content, also called Blackwater treatment, is advisable. This water helps to soften water and lowers buffering capacity. On the contrary, increasing buffering capacity with the aid of crushed coral is effective.

Use Tap Water Conditioners

Most people use tap water to fill their aquarium after it has gone through treatment. Tap water often requires aging in order to get rid of harmful substances, even though heavy metals are still a problem. This is where water conditioners are useful; they break heavy metals and disrupt their activities.

Using tap water conditioners as its benefits as it has a constituent that helps to improve fish slime coat. In fact, it helps fish cool down when they are stressed. In general, water treatment and conditioning should be done every time water is changed in the aquarium.

Final Thoughts

Always try to maintain your aquarium by checking oxygen levels in order to have good, healthy fish. Also, try to improve the living condition of fish by using safe and effective methods. Having an aquarium requires a lot of hard work, but the benefits thereof are always satisfactory.