How to Increase Oxygen in Fish Tank? (11 Proven Ways to follow)

How to Increase Oxygen in Fish Tank by Aquarium Tales

How to increase oxygen in fish tanks? You probably want to get the answer straight away. However, before that, you must know if there is really any need to boost the oxygen concentration in your aquarium. 

Guess what? A low oxygen level in the fish tank can cause difficulties for your fish to breathe, eventually lead to death. However, fish may also die because of high oxygen levels. Surprising! Although it’s rare to happen in home aquariums.

High dissolved oxygen causes Gas Bubble Disease; bubbles form to their fins, gills, and eyes. When it goes to the heart, fish die suddenly. 

Therefore, a safe oxygen level is mandatory for healthy fish. If you lack enough oxygen in your tank, you should take proper measures to increase oxygen levels.  

Here, to help you, I’ve come up with eleven ways you can follow to increase the oxygen level in your fish tank. Some are natural methods that don’t cost you a single dollar, but others will cost you a few bucks.

Symptoms of Low Oxygen Levels in the Fish Tank?

Apart from testing your fish tank’s dissolved oxygen level, there is no easy way to understand a low oxygen situation. Fishkeepers usually anticipate by closely observing the fish behavior. When the tank oxygen level is low, fish will manifest some visible signs. Let’s see what you should look for to figure out low oxygen saturation.

Gasping on the Surface

Oxygen enters the water through air-water contact at the surface of the fish tank. On the surface, the oxygen level is relatively high compared to the bottom. When the oxygen level goes down, it is evident that fish will come near the surface and try to take oxygen.

Therefore, when you see fishes are gasping near the surface, it could be an indication that your tank lacks the necessary oxygen.

However, don’t be confused with the movement of labyrinth fish. Some fish, including Bettas, Gouramis, and bottom feeder catfish, periodically come to the surface and gulp air with their labyrinth organ. They will not stay long on the surface when it’s normal.

If you notice they are also trying to take breath after breath with a wide-open mouth, including other fish, you should immediately take action.

Fish Behavior in A Low Oxygen Tank

Sluggish Fish Movement

Oxygen is the fuel to run for all living animals. Low oxygen levels will slow down fish’s natural movement. They will move less vigorously, and there will be no playful nature. Although fishes don’t move continuously, sometimes they take rest or even sleep. Still, when you see it often, that may be a symbol of low oxygen.

Lack of Appetite

In a low oxygen condition, fish will not take their bite as they usually do. So if you observe, all the fishes in your fish tank are not eating, and foods are floating on the Surface during mealtime, that may be a vital sign.

Difficulties in Breathing

In a normal situation, fish takes in water and passes back to the gill bars and gill filaments, where oxygen and carbon dioxide exchange occurs. 

At an extremely low dissolved oxygen level, fish tends to breathe desperately. Gill’s movements become rapid in an attempt to process more water to get oxygen. Excessive gill movement and troubled breathing is a clear indication of low oxygen. 

How the Oxygen Dissolves in A Fish Tank?

Oxygen gets dissolved in the water in three ways:

  • Diffusion from the surrounding air. 
  • Through aeration (rapid water movement).
  •  Photosynthesis process by plants.

A gas exchange continuously occurs on the water surface with the surrounding air called diffusion. Oxygen from the air enters the water swapping the carbon dioxide. This process becomes more vigorous when there is enough water movement, either manual or mechanical. 

Another great source of oxygen is the underwater live plants. Photosynthesis is the process by which plants utilize lights and carbon dioxide to produce food for themselves. As a byproduct, they also produce oxygen that remains dissolved in the water.

How Much Oxygen Do Fish Need?

The safe level of oxygen varies according to fish species. For example, bottom-dweller fish requires 1-2 mg/l of dissolved oxygen to survive, although many fish species require much more than that. The widely accepted DO level is 4-5 mg/L, and below three mg/L, even the hardy fish may suffocate. 

Safe Dissolved Oxygen Level

However, as I mentioned earlier, fish may die because of over oxygenation. Water can hold oxygen until it gets saturated. When saturated, oxygen can’t dissolve anymore. Fish can live happily without any complaint in oxygen-saturated water. 

But the problems arise when water becomes supersaturated. Although the occurrence is not so frequent, it does happen, and it’s one of the root causes of gas bubble disease. 

Healthy aquarium water should have an 80-110% of oxygen saturation. A significant amount of fish death occurs when dissolved oxygen rises above 115-120% for some time

What Are the Causes of Low Oxygen Level?

Knowing is winning the battle! You already know the signs of low oxygen levels in your tank; now, I’ll tell you the causes. If you identify the reasons for your problems, it won’t be hard to resolve the issue. So, let’s go ahead.


Overstocking is the most common cause of low oxygen. Too much population will obviously need more resources to survive. An aquarium is a fixed space; if you don’t stock in the right amount, there will be a shortage of oxygen. 

Beginners usually make this mistake when they start, and overstocking also lead to so many other problems.

High Water Temperature

There is a direct correlation between high water temperature and low dissolved oxygen (DO). Coldwater can hold much more oxygen than warm water. As the temperature increases, the ability to carry oxygen reduces. 

Look at the table below for a better understanding. Dissolve oxygen becomes zero (0) when the water temperature reaches 100°C (212°F). Image source:

Table for Relation between dissolved oxygen and temperature

As I said earlier, the accepted minimum level of DO is 4-5 mg/L for fish to survive. Most tropical aquarium fish live comfortably in the range of 75° to 80°F. Coldwater fish prefers below 70°F. 

So if you are using a heater, you don’t need to raise the temperature above 80°F unless you have an Ich outbreak, where a maximum of 86°F is recommended.

Waste Accumulation

Excess waste accumulation is another cause of low oxygen levels. Overstocking, overfeeding, lack of maintenance, and improper cleaning are the predominant factors for waste pile-up.

More fish will produce more waste through respiration and feces. Uneaten food due to overfeeding and clogged filter also contribute to garbage accumulation. Bacteria need more dissolved oxygen to break down the residue and waste, reducing the aquarium’s water oxygen-carrying capacity.

Suppose bacteria fail to break down the extra garbage. In that case, that will decompose and form toxic gases like ammonia, which drives away the oxygen and is lethal to fish.

Heavily Planted Tank with Low Lighting

We all know that plants bring tremendous benefits to the aquarium, including better oxygenation, however, only under the right conditions.

Plants consume carbon dioxide in the water and release oxygen in photosynthesis when exposed to sufficient light. However, when there is low or no light, the reverse process happens, they consume oxygen and release carbon dioxide.

Algae also work in the same way as live plants; therefore, the right amount of lighting is mandatory to check algae growth and maintain a healthy oxygen level. 

Lack of Water Movement

Stagnant aquarium water is another reason for low oxygen levels. As stated above, aeration (rapid movement) is one of the ways oxygen enters the water. 

Oxygen is usually rich near the surface, but that doesn’t reach the bottom due to lack of agitation or circulation. The movement of water is helpful to oxygenate the entire aquarium water volume.

Use of Certain Chemicals

The use of chemicals and additives can have an impact on low oxygen levels. Therefore, a good practice is always to be retrospective whenever you use any chemicals in your aquarium.

How to Increase Oxygen in Fish Tank Without Pump (Naturally)

1: Water Change (50%)

A water change will replenish the oxygen in your fish tank. Change 50% of water using freshwater. Check my article on how to change water without killing fish.

2: Pour Water from A Height

Pour the water from some heightThe more the height, the more the oxygen will get dissolved during the process. Next, use a container, take some of the existing water from the aquarium, pour it down, and repeat the operation several times. 

You can also do that while adding new water during a water change. Again, place a plate or bowl on the substrate to prevent stirring.

3: Manually Agitate the Water

Agitate the water manually, repeat the process from time to time. Stirring up the water surface is an excellent way to increase the oxygen level.

How to Increase Oxygen in Fish Tank During an Emergency

Your fish may need instant oxygen during emergency events, likely they are:

  • High water temperature due to heater malfunction
  • Power outage

However, regardless of the reason, if you need an immediate boost up of the oxygen level, following the below-mentioned ways will definitely help.

Method-1: Ice Cubes and Fan

If the low oxygen level is because of high temperature, along with water change and pouring water, add ice cubes in the aquarium to lower down the temperature quickly. 

Use zip-closed bags filled with ice cubes, then put them inside the water. You can also deploy a fan to increase the air circulation across the tank’s water, helping take the heat away.

Method-2: Battery Powered Air Pump

Use a battery-powered air pump if your oxygen level decreased during a power outage. Also, if you live in a place where a power outage is expected, you had better keep a battery-powered air pump for emergency support.

Although they are not as powerful as electric-driven air pumps, they could be pretty handy to handle difficult times. If the power cut occurs for a prolonged period while your filters aren’t running, in that case, you must check for ammonia. If ammonia starts showing, use ammonia reducing agents to prevent ammonia poisoning.

How to Increase Oxygen in Fish Tanks? (Permanently)

As you already know reasons for low oxygen and the impact of low oxygen on your fish. Therefore, solve the causes and try to maintain proper oxygen levels all the time. Below are the six ways to increase the oxygen level permanently. 

Step-1: Solve Overcrowing

Solving overcrowding will help you tremendously; follow the proper guideline for stocking. You should find what would be the ideal number of fishes for your aquarium.

Although there is so much controversy about the ‘one-inch rule’ — allowing one gallon of water for every inch of fish — it’s a good one to follow. First, remove extra fish from the fish tank.

Step-2: Always Keep In Check The Water Temperature

It would help if you always checked the water temperature since dissolved oxygen level decreases with increasing water temperature. High water temperature can occur due to three reasons:

  • Heater malfunction
  • The aquarium light heated the water
  • The aquarium is exposed to direct sunlight
  • Very high ambient temperature (Likely in summer)

I heard so many horror stories of a faulty heater that led to fish death.  Nowadays, many reliable brands over there, but you can’t knock it out. 

To prevent accidental temperature rise because of heater malfunction, I recommend using a separate temperature controller along with the heater. If one fails, the other will catch it up. This added safety will give you a permanent solution.  

Some aquarium lights heat the water, i.e., fluorescent bulbs, metal halides. However, you can buy LEDs instead of using those lights because LEDs don’t heat the water. Check my article for the best-LED lights for aquariums

Moreover, you should not place your aquarium under direct sunlight; it makes the water warm and leads to algae problems. Your aquarium should be in the coolest place in your home. 

During summer, the ambient temperature goes high. Suppose you live in a place where it’s challenging to restrain the tank temperature in a desirable range. In that case, an aquarium chiller could be a good solution.

Aquarium chillers are a great way to keep your fish cool and happy. They work by transferring heat away from the water and into the air or ground surrounding the aquarium. The cooler temperature will then result in a more comfortable environment for your fish, as well as increased oxygen availability.

Step-3: Keep Aquarium Clean & Improve Water Quality

Improving water quality in your fish tank is a great way to keep them happy and healthy! To do this, you’ll need to replace 20% every week, and you can also help by making sure any old food at the bottom gets removed.

This will eliminate excess organic materials from your aquarium environment, which can cause high concentrations of ammonia and nitrites if not removed timely. Not only does it will keep aquatic friends alive but also making their home more livable while reducing the waste build-up over time.

Routine cleaning of fish tanks and maintenance of your filter is another way to prevent waste build-up. Whatever filter you are using, follow the manufacture’s guidelines to replace the filter element to avoid clogging. 

Cleaning the aquarium is a painstaking task to do. I don’t want to elaborate here. I have a detailed article on how to clean a fish tank; please check that out. 

Step-4: Create Surface Agitation And Water Movement

Providing better air-water contact and water movement are the most effective ways of increasing oxygen in a fish tank. I’ll suggest several ways that you can implement. You don’t need to use all of them, either one or two.

HOB filter

HOB Filter

HOB (Hang On Back) filters are great for increasing air-water contact, usually sit on top of your aquarium at the rear end. The filtered water from HOB cycles back to the aquarium like a waterfall, which helps to aerate the water. 

They also circulate the water, distribute the oxygen all through the aquarium. If you plan to buy a HOB filter, check out my article, Best HOB filters, to create a thriving aquarium. 

Aquarium Spray Bar

Spray Bar

A spray bar is an excellent option to increase dissolved oxygen. A spray bar is a sprinkler tube attach to the canister filter’s outlet and evenly sprays the water across the aquarium surface from a height. As a result, water en route to the aquarium comes into contact with air and allows more oxygen to enter. 

The spray bar also creates surface agitation, which oxygenates the aquarium water. A spray bar usually comes with a canister filter package. However, if your canister doesn’t have one, you can easily set a spray bar separately at the filter outlet. Check it out; I’ve found a good spray bar for you. 

Air pump with air stone

An Air pump & Bubbler

Most people who use some sort of aquarium filter, usually don’t use an air pump separately. Many also don’t like the tubings associated with air pumps because of visual appeal. But an air pump along with an air stone/bubbler will solve your low oxygen problem straightaway.

The complaint is air pumps are not so reliable and create irritating noise. No worry, just for you, I have made a list of air pumps from a reliable brand that doesn’t make noise. Check my article for the best aquarium air pump

Try to keep your aquarium water level low enough so the water coming out of HOBs, powerhead, or spray bar can make bubbles. Keep the water level 3 inches below the top. However, it isn’t applicable if you use an air pump or wavemaker.

Aquarium Powerhead

Powerhead/Water Pump

Using a powerhead is an excellent way to create water movement. If your tank lacks the necessary oxygen, you can add a powerhead. 

The increased water movement by the powerhead will increase the oxygen level in your tank. A larger tank may need more than one powerhead to sufficiently oxygenating the water. 


Although some people think wavemaker and powerhead are the same. They are similar but not the same. Wavemaker is another good choice to agitate the water surface. Wavemaker creates a wave in the aquarium, like seas or oceans. The turbulence created by the wavemaker enriches aquarium water with oxygen.

Related read: Best Aquarium Wavemaker for creating wave effect in your aquarium

Step-5: Extract the Benefits from Plants

Well-managed plants could be a great source of dissolved oxygen for your aquarium. Therefore, if you have live plants, you should know how to extract the benefits from plants. Otherwise, plants will do more harm than good in terms oxygen concentration of your tank. 

  • Ensure proper lighting throughout the tank; it will help plants to grow by photosynthesis, and as well as you will get dissolved oxygen. 
  • Keep in check algae growth; never leave your lights on all the time.

Step-6: Read the Labels

Since chemicals can alter oxygen concentration, always read the label before adding chemicals or additives to your aquarium. Stop using anything that interferes with oxygen level.

Take Away

Hopefully, now you have a much better understanding of the overall concept. So, how to increase oxygen in a fish tank? In a nutshell, you can instantly improve the oxygen level by pouring down some water in the aquarium from a height. Then, a significant water change (50%) or manual surface agitation effectively boosts the oxygen level. 

However, those are temporary; you can use an air pump, powerhead, or HOB filter to get the permanent solutionI have mentioned several permanent solutions; however, you don’t need all of them, maybe one or two. 

A properly maintained aquarium usually doesn’t show symptoms of low oxygen. Everybody wants to provide a comfortable living place for their adorable fishes. However, a low oxygen level is devastating. I suggest using one of the permanent solutions to avoid the risk and always be prepared for the emergency.

I would like to hear your experience and opinions on how you dealt with the low oxygen problems. If you have followed my suggestions, what method do you find most compelling? Would you mind leaving a comment below?

2 thoughts on “How to Increase Oxygen in Fish Tank? (11 Proven Ways to follow)”

  1. Improving the water quality in a fish tank is an important step for increasing oxygen levels and keeping your pet happy. To do this, you’ll need to change 20% of the total amount of water every week as well as replace any old food that might have been left sitting at the bottom with new, fresh produce. This will remove excess organic matter from both environments which can cause high concentrations of ammonia or nitrites if not removed on time! Not only does it keep our four legged friends alive but also helps make their home more habitable while reducing waste buildup over time.

    1. Hi SHUNCY,

      It is a good point that needs to be added. Yes, indeed, if you keep changing a potion of water every week, that will keep the water parameters in a reasonable range. And leftover foods are dangerous, the proper amount of feeding and adequate filtration are necessary for that. Thanks.

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