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How to get more oxygen into your fish tank without pump; 5 ways to

How to get more oxygen into fish tank is an occasional worry you might have to address. Well, occasionally. Why you ask? Because fish, just like you need sufficient oxygen to survive. Sufficiency of oxygen in fish tank isn’t always guaranteed. Your intervention is therefore needed.

It is for that reason, aquarists have air pumps in their fish tanks for adding oxygen. However, some aquariums, whether by design or otherwise, pumps may not be present or functional. For such reasons, it’d help if you knew how to increase oxygen in fish tank even without a pump.

How to increase oxygen in fish tank without pump
Bubbling agitates the water 💦 surface for gases exchange

In most cases, decision on not having an air pump for aerating an aquarium is made even before tank set up.

This could be thanks to unavoidable limitation(s) or by choice.  Either way, the issue of “how to aerate aquarium water” must be predetermined beforehand.

Having said the above, oxygen levels in the fish tank should neither be too high nor too low.

How do fish breathe?

First and for clarity, the atmospheric oxygen breathed by humans is essentially similar to what fish breathe in the water. And just like sugar or salt dissolves in water, so does it.

Water is however way denser and more viscous than air. As a result, oxygen therein is about 5 – 10% less than in the air.

Further, fish unlike humans need more energy in breathing; well, for extracting oxygen by pumping water through gills.

Subsequently, its feather like filaments in its gill structure extracts about 70 – 80% of oxygen in the water. The extraction is way effective than of the human’s lungs at a measly 25% extraction of the air breathed.

The surface’s consistency in air content is humans only safety net. This is not the case for fish though.

The aquarium dissolved oxygen levels will unfortunately vary as the aquarium’s environment changes. This fluctuation can therefore be a big source of stress to your fish.  

So, how much oxygen do fish need?

You may not know this but too much oxygen has its perils on the fish; similarly, low oxygen too.

In addition, different fish have varying oxygen needs. As such, there really isn’t a concrete and definite answer. For instance, small sized fish need lesser oxygen/hour compared to bigger once. The same is also true of fast swimming fish compared to slow swimmers.

Efficiency of getting oxygen to body tissues is particularly a great trait with goldfish. As a result, unlike most other species, they can cope in low oxygen conditions and for long. Others have labyrinth organ which helps them get air from the air surface. Subsequently, they are able to survive comfortably in low oxygen aquariums.

From some studies (in particular by FWS) however, ideal dissolved oxygen levels for most is about 5PPM (parts per million). Further, fish will start suffocating if it drops to dangerous levels of below 2PPM.

So, how do you measure oxygen levels in the aquarium?

Well, oxygen test kits are available in the pet stores or online. This test kit is not too expensive.

However, the more accurate portable dissolved oxygen meter is also an option. While it maybe pricey, you won’t regret having it.

Can too much oxygen in fish tank harm fish?

If you be asking “can you have too much oxygen in a fish tank?” the answer is yes.

Moreover, if you’re asking “can too much oxygen can hurt my fish?” sadly the answer is yes. Gas bubble disease (GBD) will afflict your per fish if aquarium oxygen levels are too high.

The bubbles forms round the body, including on eyes, fins and even gills. This trauma is however non-infectious. It results when the dissolved gas is above the ambient air pressure.

Generally, any trauma will cause your fish stress. As a result, stress will undermine its immunity exposing it to other illnesses that could lead to its demise.

What are the signs of low oxygen in aquarium?

If the tank suffers oxygen insufficiency, the fish will definitely alert you. They “don’t mince words”. Well, albeit under severe distress.

When you note theses signs, it’s time you engaged your skills on how to increase oxygen in the fish tank even without a pump.

Fish swimming at the water surface gasping:

It’s not always fish swimming at the surface with wide open mouth is a sign of hunger. NO!!! In most cases, it’ll be trying to catch some breath. Nonetheless, fish will occasionally swim at the surface.

However, if it is sustained more than is normal, your aquarium is suffering a dire oxygen shortage.

It is even a dire case when normal bottom tank dwellers have to come up to the surface to breathe.

Difficulty in breathing:

Rapid gill movements are signs of a labored breathing. This mostly results when aquarium oxygen levels are unsafely low.

Lethargy in fish:

The severe suffocation stress will make the fish lethargic. Subsequently, you’ll note less movement as well as feeding.

In short, they’ll have abnormally long rest periods.

Factors causing low aquarium oxygen levels; to guide appropriate tank aeration means:  

It’s important you correctly identify what is causing oxygen shortage in your tank. Following that therefore, you can then decide on the best fish tank aeration system for your aquarium.

Common factors that cause aquarium oxygen shortage include:

Lack or minimal water movement:

Water movement enables aeration throughout the fish tank. As a result therefore, if it’s minimal or nonexistent, some tank sections will automatically suffer oxygen shortage.

In addition, lack of a working or inefficient mechanism on how to agitate water will also cause drop in dissolved oxygen amounts.

Water surface needs to be agitated/disturbed to allow oxygen exchange and addition/absorption in the tank.

Increase in tank temperatures:

Warm water is known not to hold as much oxygen as cold water. It is for this reason that consistency in tank’s temperatures is critical.

Besides, fish are cold blooded. Therefore, aquarium water should maintain appropriate temperatures.

Chemicals in the water:

Medications added to the water form a sheet like film cover over the water surface. The impenetrable film inhibits exchange of oxygen from the air surface.

This subsequently will reduce oxygen in your fish tank. It needs to be broken.

Besides, many medication chemicals extract oxygen from the water. This causes aquarium oxygen shortage just as raising the water temperature does when used as treatment alternative.    

Fish tank overstocking:

You should match your pet fish stock with appropriate aquarium size. A big stock in a small aquarium will obviously result in low oxygen levels.

Having known the effects of low oxygen levels, it’s now time to know how to add oxygen to fish tank.

Now, let’s talk how you can effectively do it without an air pump.

How do you increase oxygen in fish tank without air pump?

You should know how to oxygenate a fish tank without a pump easily incase of emergencies like pump malfunctions or power outage. If the pump is not there by choice too, knowing how to do is critical in keeping fish alive.

So, whatever the case, let’s check out what to do:

The cup method:

Top of the list on how to add oxygen to water sits this manual way. It shouldn’t amaze you that a cup or a pitcher can be used for natural aeration of water.

Just scoop the aquarium water in a clean cup, jar/pitcher and lift it high above the tank. Now, from a good height, pour the water back into the tank.

Repeat this for as many times as you consider enough. Well, a “few” times won’t hurt.

The rationale here is, from the air surface, the water will pick oxygen as it pours back.

How high the water is falling from will determine how much of air it can pick.

In short, more water exposure means more oxygen pick-up. Subsequently, the collected oxygen is added to the tank waters.

Caution however is that, you are likely to disturb the substrate as the water pours into the tank.

To avoid this, just immerse a bowl or plate into the aquarium. It’s meant to sit on the substrate. Therefore, it should be sufficiently heavy not to float. The pouring water should be over the area where the plate sits.

Using a powerful filter:

It can be very helpful as a fish tank aerator. As the water flows through it, it picks oxygen which it then injects in the water.

Following that therefore, a high flow rate enhances more oxygen collection. This is because of sufficient water surface agitation. You therefore need a powerful filter for that.

A substantial water change:

This is another of inexpensive but reliable means on how to increase dissolved oxygen in the aquarium. Obviously, freshwater will have more dissolved oxygen. Now, if you do, say a 40-50% water change, you’ll substantially increase oxygen in the fish tank.

Adding aquarium plants:

Adding aquatic plants is a rather easy and natural aeration of water method. Besides, it’s also being a great way of adding aesthetics to your tank. For a bonus, your fish get nice swimming and hiding areas.

As photosynthesis takes place, these plants take up carbon dioxide and in-exchange, generate oxygen. (See some great floating aquatic plants here)

More plants will obviously generate more oxygen. The good thing is plants will be well spread out in the tank. Therefore, there is no challenge in the generated oxygen’s circulation.

Using a fish tank with a wide surface area:

This is ideally not an intervention measure. It is rather by design and decided on prior to tank set-up. It’s perhaps the best way to aerate a fish tank without a pump.

Remember we said some aquarist choose not to have a pump. You too can choose not to have one. If you do, ensure your fish tank has a wide open surface.

Besides, it should be shallow but sufficiently deep to safely cover the fish.

At or near the surface, oxygen concentration is high and the opposite is true.

It follows therefore that, more water surface contact with air surface means more oxygen dissolved in water.


About 2 days is just about how long a fish can live without oxygen. On the flip side, too much oxygen will cause gas bubble disease to your fish.

Therefore, the right amount should be maintained always. It is for this reason that you should learn how to increase oxygen in a fish tank even without pump. It will save your fish even in emergency times or when you overstay your travel.

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