How Can I Keep A Very Small Tank Well Oxygenated?

By Nadine Oraby | 2020 Update


Keeping more fish in a small tank is a bad idea.

But if you still need it to be this way, then you need to oxygenate your tank efficiently.

So how do you oxygenate your small tank?

Use a filter. This helps break the surface of the water which is the basic way to oxygenate a still water body. You can use some decorations that help oxygenate your tank. Some water plants can also be used. Keep testing your water for ammonia and toxic materials. Air pumps can be used as well.

Keep reading to find more information on all the methods to keep your tank oxygenated.

Ways To Oxygenate Your Tank

It does not matter what is the size of your tank, you always have to keep it oxygenated. So all these methods apply to any type of tank.

Emergency And Preventive Measures

If you see your fishes gasping at the surface of the water, then this means that there is an insufficient amount of oxygen in the water.

Steps should be taken even if only one of your fish is acting this way:

  • Do a water change in your tank. You will need to change as much as half of the water.
  • Add an additional filter to increase the water movement. This will help the oxygen exchange.
  • Perform water quality test more often to detect an underlying problem.

Use A Water Filter

This is the most basic thing that every fish tank owner does. It breaks the surface of the water to let the oxygen in.

The filtered water is dropped back at the surface of the water, which helps put some oxygen back in.

Using Decorations

There are some decorations that help in putting some oxygen in the tank water.

You must have seen the treasure chest decoration. With some intervals of time, its lid opens up and spills out bubbles. These types of decorations are called aerating decorations.

You can buy such types of decorations from the pet shop.

Use An Air Pump

As indicated by its name, an air pump drives air into the fish tank to balance the amount of oxygen. You can use battery-powered pumps.

But battery-powered pumps do not pump the air too far in the tank. So you will need to check either the pump would be of any help in an emergency or not.

Oxygenate The Water Yourself

You can oxygenate the water yourself by changing it or by using the following method:

  1. Take a clean container and fill it with some water from your aquarium.
  2. Now holding the container above some distance from the tank, slowly pour the water back into the tank.
  3. What this will do is that the water will catch air while falling into the tank and would provide the tank with the oxygen.
  4. Repeat this several times.
  5. Higher the distance of the filled container while pouring the water, the higher the amount of added oxygen.

You can do this whenever you feel doubt or when you see your fish gasping for air on the surface of the water.

Watch this video to learn how to add oxygen in a fish tank:

So these were the ways you can oxygenate your tank.

But what is the cause of low oxygen in an aquarium? And what happens with there is too much oxygen in a tank?

Continue reading to find out!

What Causes Oxygen Loss In A Fish Tank?

Water Movement

The tank water needs to have oxygen exchange to oxygenate the tank water. The water will lose oxygen if it is not moving sufficiently.

This is what filters are used for. They help in water movement, causing the exchange of oxygen.

Filters also help in distributing oxygen as it moves the water from top to bottom.

You can use any other aerators that helps in the water movement. Adding a water fountain or a wavemaker will help too.

Overcrowding And Waste

This is the most possible reason for low oxygen especially in small tanks. Fishes need a certain amount of space for them to live or they might become overstressed and die.

As told at the start of this article, you need to consider buying a bigger tank. Because it’s very dangerous to keep too many fish in a small tank.

There are some bacteria present in the filter of an aquarium. They help in keeping the water clean by eating on the waste or decayed bodies of dead fish.

But in a small tank, the amount of bacteria present is not sufficient. So the water is not cleaned properly and the amount of oxygen decreases.

High Temperature

The temperature of the tank water needs to be balanced for the fish to live in because you do not want to boil your fish!

But other than that, the temperature does not need to be too high because high-temperature water cannot hold as much oxygen as cold water.

What you need to do is while changing the water is that change the water with lower temperature water which will put fresh oxygen in the tank.

There are some things you can do to lower the temperature of water:

  • Turn off the heaters.
  • Blow air across the surface of the water.
  • Put a zip lock bag with ice cubs in the aquarium.

Other Causes Of Oxygen Loss

  • Chemicals: some chemicals used to treat a disease can affect the water to lessen the capacity of oxygen in it. Use such medicines wisely.
  • Waste: excessive waste, algae growth and clogged filters can decrease the oxygen. Clean the tank thoroughly to avoid this. Watch this video to learn how to clean a tank:
  • Plants: when plants are exposed to light, they give off oxygen. But when it is dark, the plants will consume oxygen to stay alive. This will decrease the amount of oxygen for your poor fish.

Extra Oxygen In An Aquarium

Here’s the deal:

You might be worried about your fish that they are not having a sufficient amount of oxygen.

But the struggle to introduce oxygen inside your tank can cause harm to your fish!

Having too much oxygen inside your tank will lead your fish to get a dangerous disease called the bubble disease.

The over-oxygenated water drain out of the fish’s bloodstream and make bubbles on their body which will be visible on their fins, gills and eyes.

But it gets worse:

The bubbles can also get built up in the fish’s heart and can ultimately lead to death!

So be very careful and do not over oxygenate your tank.

Related Questions

How can I get more oxygen in my fish tank without a pump?

Water movement provides more oxygen to a fish tank. And if you do not have an aquarium with a pitcher, you can use the container method. Just simply take the water from the aquarium in a container. Now raise the container high above the tank and then pour the water back into the tank. The water will catch oxygen on its way down.

Is too much air bubbles bad for fish?

It is bad for your fish as more oxygen in the water will lead to your fish getting the bubble disease. Because of this disease, you will see visible bubbles on the skin of the fish. The bubbles can form near the heart of the fish and can cause death.

Do air stones oxygenate water?

Efficient water circulation is good to oxygenate the water. And air stones provide that circulation of water. So air stones do help in oxygenating the water but the use of an air pump is a better option.

Why are all my fish at the top of the tank?

Fish start swimming at the top of the tank to grasp oxygen. This happens when there is less oxygen in the tank and fish move to the surface of the water to get the oxygen because there is a higher level of dissolved oxygen present at the top of the tank.


Now I hope that you know all about oxygenating a fish tank. But as told earlier, try to buy a larger fish tank.

To know how much big you want your new tank to be, use the rule of one gallon of water for every inch of adult fish.

So for example, if you have 6 fishes and your current tank which can hold about 4 to 5 gallons of water, then your new tank must at least be able to hold 6 to 7 gallons of water for your fishes to live freely. Good Luck!


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