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How To Get More Oxygen In Your Fish Tank: 6 Causes & Solutions

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By Lindsey Stanton

colorful fish in tank with bubbles

Oxygen is a very important aspect that needs to be present in any fish tank. The bottom line is that fish cannot survive if there is no oxygen in the water. Low oxygen levels can cause health issues and can be very deadly to your fish.

Several different factors can contribute to low fish tank oxygen levels, but thankfully there are also several fixes for this issue. Today we want to talk about how to get more oxygen in your fish tank and simple solutions to fixing low oxygen levels.

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How To Increase Oxygen In Your Fish Tank

aquarium filter nozzle with bubbles
Image Credit: Lapis2380, Shutterstock

The short answer is there are a variety of ways to increase aquarium oxygen levels, these include;

  • Get an air pump
  • Get an air stone
  • Use a filter with a waterfall feature
  • Add more plants to your tank (the right ones, covered below)
  • Decrease the number of fish in the tank

How Do I Tell If Oxygen Is Low?

Ok, so unfortunately there are no alarms or big sirens that will go off then the oxygen levels in the fish tank are low.

One of the easiest ways of telling if there is not enough oxygen in the fish tank is simply by getting a testing kit (this is a good test kit) and measuring the amount of dissolved oxygen in the water.

However, while it may not be all that easy or crystal clear, you can tell if there is not enough oxygen by the behavior of your fish.

Signs of Low Oxygen In Aquarium

If there is not enough oxygen in the fish tank, your fish will start to become sluggish and move around a lot less.

The low oxygen levels will make the fish slow, sluggish, swim slowly, and not eat much either. You will also notice that the gills of your fish begin moving excessively fast in a vain attempt to suck up enough oxygen to survive.

In other words, they will have trouble breathing, something that you should be able to tell by looking at them.

If the oxygen levels get to a critically low level, your fish will begin to come to the surface of the water to get oxygen from the air above the tank.

Some fish go to the surface for feeding, as well, some labyrinth fish will also surface and take a breath now and then.

However, if all of your fish are surfacing and gasping for air with a wide-open mouth, you know that there is not enough oxygen in the tank anymore.

If you notice any of these things happening, you know that the oxygen level in the tank is way too low and you need to take action as soon as possible.

co2 bubbles in tank aquarium
Image Credit: Chaikom, Shutterstock

The 6 Causes & Solutions of Low Oxygen Levels

Several different factors can cause low oxygen levels in the water, but each of them has a pretty easy solution. It could be a combination of factors, so let’s review those now.

Adding some air stones into the filter and adding an air pump for increased oxygenation are always options you can consider.

They might just be the best solutions, especially because they will help mitigate all of the problems we are about to talk about.

1. Overcrowding

Simply put, fish need to breathe oxygen, but a fish tank of a certain size can only have enough for a certain amount of fish.

In other words, if you have too many fish in the tank and the aquarium is overcrowded, it’s like a fight for oxygen between your fish. There are simply too many fish in the tank to be accommodated in terms of oxygen.

The solution to this problem is to have fewer fish in the tank, but since you probably don’t want to kill any fish, you can always upgrade to a larger tank.

You could also separate the fish and house them in more tanks than one. This should help too. Of course, air stones (we have covered our top 5 here) and air pumps can help a whole lot with this problem too.


2. A High Water Temperature

Another thing that can be the cause of low oxygen levels in the water is if the water temperature is too high.

If you did not already know, warm water can hold a lot less oxygen than cold water. Now, this might be a bit of a tricky problem because some of your fish or plants might require really warm water to survive.

However, for instance, if the water is at 80 degrees, but your fish only need 75 degrees, you can take some steps to lower the water temperature. For instance, you can perform a water change of 25% or 50% using cooler water.

You can also put a few ice cubes in a plastic bag and place them in the aquarium. Another thing that you can do is to turn off all of the lights and heaters in the aquarium and of course, make sure you have a good thermometer so you can keep an eye on the temperature.


3. Too Much Waste

If you have too many fish in a single tank, they will produce a lot of waste, and the ammonia and nitrites which the waste releases cause a depleted oxygen level.

It makes the water unable to hold as much oxygen. At the same time, having too many algae in the water also decreases the oxygen-carrying capacity of the water.

The easiest solution to this problem is to do a water change and to clean the tank. Cleaning all of the waste out of the tank should increase the oxygen-carrying capacity of the water. Cleaning the filter should help with this too because it will help the filter remove more waste from the water.

 

colorful cichlids swimming in tank
Image Credit: andreibucataru.ro, Shutterstock

4. Not Enough Water Movement

If the water is stagnant and there is not a lot of water movement, it will also cause low oxygen levels in the water. This is especially true the lower down in the tank you go because there is no oxygen exchange going on.

Yes, the water near the surface will absorb oxygen out of the air, so the surface probably has quite a bit, but because there is little or no water movement, that oxygen does not get transferred to lower down depths. A good way to solve this problem is to have a good filter, one with a high flow rate and a powerful output pump.

This will cause the water to move around and will help in terms of oxygen exchange from the top of the tank to the bottom. The problem can often be solved by cleaning a filter that is not running at full capacity, or conversely, you might need to invest in a more powerful filter.

A water pump to create some movement will help too. Of course, an airstone or air pump will help as well. A powerhead or spray filter to send the water down further once filtered will assist with water movement and oxygen exchange as well.


5. Too Many Live Plants

Ok, this might seem a little odd, because when there is light, plants absorb CO2 out of the water and produce oxygen. However, when the lights are off, the opposite happens, with plants absorbing oxygen and producing CO2, which of course makes it harder for your fish to breathe.

So, you can take some plants out of the tank, which should help. Adding a few extra hours of light per day will help the plants absorb more CO2 and produce more oxygen.

The best bet is to remove as many algae from the water as possible (we have covered a separate guide on that over in this article).


6. Chemicals

On a side note, chemicals used to treat the water for one reason or another can also harm oxygen levels in the water.

Whenever you add any chemicals or solutions to the water, read the label and make sure that it does not adversely affect dissolved oxygen levels in the water.

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Commonly Asked Questions: Fish Tank Oxygen

Can You Have Too Much Oxygen In A Fish Tank?

Yes, indeed there can be too much oxygen in a fish tank. There is a sickness that can develop, called gas bubble disease.

This is when gas comes out of the solution inside the fish, and these air bubbles can then build up under the skin and around the eyes, which can end up being lethal.

So always ensure that your fish tank has enough oxygen, but not too much. Freshwater fish need the oxygen level to be at 8.3 parts per million, while it’s between 6.4 and 7.0 parts per million for saltwater fish.

How Much Oxygen Does a Fish Need?

Fish need to have a certain amount of dissolved oxygen in the water to survive.

Some water-dwelling creatures, such as crabs, worms, bottom feeders, and other such bottom dwellers require between 1 and 6 mg of oxygen per liter of water.

Fish that live in shallower waters require more oxygen in the water, anywhere between 5 and 15 mg per liter.

How Long Can a Fish Survive without Oxygen?

The short answer here is not very long. A fish may be able to survive in water without oxygen or with very low oxygen levels for up to 2 days, but even this is a stretch.

If there is no or low oxygen in the water, you will notice your fish displaying symptoms (such as gasping for air at the surface), very quickly.

What are Good High Oxygen Producing Aquarium Plants?

  • Water wisteria
  • Java Fern
  • Java Moss
  • Amazon Sword
  • Green Tiger Lotus
  • Arrowhead
  • Eelgrass (Vallisneria)
  • Fanwort
  • Hornwort
  • Water Sprite

Can Too Much Oxygen Kill Fish?

Yes, as mentioned above, too much oxygen in the water will lead to a gas bubble disease which can kill fish, fairly quickly at that too.

Always be sure to measure oxygen levels in your aquarium if you think there may be too much.

How Do I Check The Oxygen Level In My Fish Tank?

The fastest, easiest, and most reliable way to measure the amount of dissolved oxygen in your fish tank is to use a portable dissolved oxygen meter.

Other than that, there is no way for humans to tell. It’s not something that can be seen by eye, smelled, or felt by hand. An oxygen meter is the only solution here.

Why Are My Fish Gasping For Air?

If your fish are gasping for air, it usually means that there is too little dissolved oxygen in the aquarium.

Sometimes gasping can be a sign of other illnesses, as well as improper water temperature, usually water that is too hot. Although, 99% of the time, a gasping fish needs more oxygen.

aquarium background plants
Image Credit: Vladyslav Starozhylov, Shutterstock

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Conclusion

The bottom line here is that one way or another, you need to solve the problem of low oxygen in the fish tank. Your fish are not healthy and they definitely won’t survive for long if they can’t breathe.

Be sure to analyze your tank, figure out what the problem is, and take adequate steps to solve the problem.


Feature Image: xzgorik, Shutterstock

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