How to Oxygenate a Fish Tank Without a Pump? – 7 Methods

how to oxygenate a fish tank without a pump

Everyone knows fish need oxygen to survive, but do you know how to oxygenate a fish tank without a pump?

There are many ways to oxygenate or aerate a fish tank without a pump, including pouring water from a height, adding ice cubes, changing large volumes of fish tank water, and manually stirring the aquarium water.

One question remains: how do you do it? Keep reading to learn proven tricks to add oxygen to a fish tank without having to shell out money for an air pump.

What Causes Oxygen Deficiency in Fish Tank?


Low levels of dissolved oxygen in fish tanks can be due to the following reasons.

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  • Overcrowding – More fish in an aquarium translates to stiff competition for oxygen. Aquarists must observe the “one-inch-size-fish-per-gallon” rule.
  • Too Many Fish Waste – Microorganisms like bacteria also require oxygen to break down organic compounds, such as uneaten fish food, fish poop, and other debris.
  • Warm Water – Water temperatures higher than 86 degrees Fahrenheit reduce the water’s oxygen-holding capacity.
  • Still Water – Stagnant water prevents the mixing of oxygen-rich surface water with oxygen-poor bottom water.
  • Algae Overgrowth – Algae get oxygen in fish tank during their active respiration at night.
  • Live Plants – Although live plants produce oxygen as a byproduct of photosynthesis, they consume oxygen when there is no light, such as at nighttime.
  • Chemicals – Some water conditioners and fish medications can influence aquarium water’s oxygen-carrying capabilities. Aquarists must research these products’ active ingredients for their impact on dissolved oxygen.


Signs of Low Oxygen in Aquarium


The only way to know an aquarium has low oxygen levels is by testing it with a dissolved oxygen meter.

However, you can observe some tell-tale signs of low dissolved oxygen, allowing you to oxygenate the aquarium as necessary.

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  • Sluggish fish movements – Fish spend oxygen every time they move. Hence, you can suspect low oxygen levels if your fish is not moving as usual, even during meal times.
  • Labored breathing – Fish will attempt to “breathe” in more oxygen by moving their gills faster (fish filter oxygen through their gills).
  • Gasping for air – You will notice your fish going to the surface more frequently to get more oxygen in a fish tank. This sign indicates dangerously low oxygen levels.


Ways to Oxygenate a Fish Tank Without a Pump

Short-term Tricks

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Trick 1: Pour aquarium water from a height.

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This short-term solution can help increase oxygen in fish tank units by agitating the water and promoting the mixing of oxygen-rich surface water with oxygen-poor lower-section water.

You will need a small container for this trick (i.e., a cup, jug, or pitcher). Scoop some aquarium water and raise the container as high as possible.

Slowly pour the fish tank water back into the aquarium, being mindful not to scare the fish. However, make sure that you create water movement and agitation.


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Trick 2: Add ice cubes to the fish tank.

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High water temperatures lower water’s oxygen-holding capabilities. Adding ice cubes is one of the most effective and convenient ways to increase oxygen levels in aquariums.

However, please do not drop the ice cubes into the aquarium as is. Doing so can produce uncontrolled water parameter fluctuations detrimental to your fish’s health.

Instead, place the ice cubes in a Ziploc bag or a similar container with an airtight and watertight seal. Submerge the “ice bag” in the fish tank for several minutes. We recommend checking the water temperature to know when to take the ice bag out.


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Trick 3: Manually stir the fish tank water.

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Here is a trick even kids can perform to fix oxygen levels in fish tank. There are no limits to what you can use to stir the aquarium water, although common sense dictates it should be safe for fish.

You can use a ladle, a long-stemmed spoon, or a broad stick to stir the water. Be careful not to hit the substrate to avoid turning the water murky.

This method agitates the water and mixes oxygen-rich and oxygen-poor water. It makes for a handy solution to add oxygen to fish bowl units.


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Trick 4: Direct an electric fan into the fish tank.

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Like the wind creating wave-like effects on open bodies of water, directing airflow from an electric fan to the fish tank can agitate the water’s surface.

Airflow does not only promote water movement. It also cools the water, allowing the aquarium to increase its dissolved oxygen levels.

Position the electric fan near the aquarium’s top and turn it on. You should see the ripple effect on the water’s surface. We also recommend checking the water temperature to know when water cooling is enough.


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Trick 5: Change 50% of the aquarium water.

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Algae overgrowth is the most common reason for low oxygen levels in fish tanks. These organisms thrive in water rich in dissolved organic compounds (i.e., nitrogen and phosphorus).

Changing 50% of the fish tank water will help put more oxygen in fish tank units by replacing half of it with oxygen-rich water. Here is how you change the water.

  1. Turn off any electrical appliances in your fish tank.
  2. Use a gravel cleaner and dip the tube’s end in the fish tank. Position the tubing’s other end in a container.
  3. Turn on the gravel cleaner and siphon 50% of the water.
  4. Add pre-treated water into the aquarium until the fish tank’s maximum fill line.


Long-term Approaches

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Method 1: Install a hang-on-back or power filter.

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Power filters or “hang-on-back” filters are an excellent long-term solution to ensure adequate fish tank oxygenation by agitating the water.

The best part about this approach is it also keeps the water clean. Power filters have superb mechanical, biological, and chemical filtration capabilities.

And since one reason for low oxygen levels is too many organic compounds in the water, you will never worry about these substances again.

Here are the steps for installing a power filter in your fish tank.

  1. Read the manufacturer’s installation instructions.
  2. Assemble the power filter by setting the filter pump mechanism into the housing.
  3. Grab the lift tube and secure it to its port on the filter housing.
  4. Prepare the filter media (wash them if necessary) and place it in the power filter housing.
  5. Determine the best location for the power filter on the aquarium and secure it with the built-in hook.
  6. Adjust the fish tank water level as necessary.
  7. Turn on the hang-on-back or power filter.


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Method 2: Install spray bars.

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Another long-term solution to low oxygen levels in fish tanks is spray bars. These devices are like sprinklers in the garden, dripping water into the fish tank to agitate the water and produce movement.

This method is perfect if you already have a canister filter because you can connect the spray bar to a port in the filter. Otherwise, you can check the manufacturer’s recommendations for how to install a spray bar in your fish tank.


What is the Difference Between Oxygenation and Aeration?


The main difference between oxygenation and aeration is their oxygen levels. Atmospheric air contains 21% oxygen (and 78% nitrogen). Hence, aeration only introduces about 21% oxygen into the fish tank.

Meanwhile, oxygenation delivers up to 99% oxygen into the aquarium water. Most aquarists make a oxygen pump for fish tank units to provide the water with such a high percentage of oxygen.

Another difference is that aeration prevents algae overgrowth, regulates water temperature fluctuations, and improves water quality.

On the other hand, oxygenation is most suitable in low levels of dissolved oxygen that can undermine fish health and safety. It can also stimulate growth and feeding in sick fish.

Helpful Tips/FAQs


How do I test for my fish tank’s dissolved oxygen levels?

You have two ways to test oxygen levels in fish tank units.

First, use a dissolved oxygen test kit, similar to a pH test strip. You only need to add a few drops of aquarium water on a test strip, wait for it to change color, and compare the color to a baseline chart.

Second, use a dissolved oxygen meter (like a pulse oximeter). Dip the probe into the fish tank water and read the oxygen levels on the screen. This method is more accurate than the dissolved oxygen test strip, although it is not maintenance-free.

Is too much oxygen harmful for fish?

The recommended level of dissolved oxygen for fish tanks is six to eight milligrams per liter or about 0.35 to 0.47 grains of oxygen per gallon. The average oxygen saturation is 80 to 110 percent. Any value above these figures is harmful, causing “gas bubble disease.”

To be specific, excess oxygen (and nitrogen) form microbubbles in the fish’s blood vessels, coalescing to produce larger bubbles. These air pockets can obstruct blood flow, leading to tissue and organ damage, as well as possible death.


You have several options on how to oxygenate a fish tank without a pump.

Short-term solutions include pouring fish tank water from a height and replacing 50% of the aquarium water with fresh water. Adding ice cubes, manually stirring the aquarium water, and directing airflow to the fish tank also help.

Although these tricks are suitable for instant oxygen spikes, a better approach is to install a power filter or spray bar to ensure long-term oxygenation adequacy.