How To Get More Oxygen Into Your Fish Tank

When you have a fish tank or aquarium, you should always be aware of the oxygen conditions in it – as having low or insufficient oxygen for the number of animals inside can pose really dire consequences. 

Typically, an inadequate supply of oxygen is not an issue in a tank that has been well and attentively maintained, and not overcrowded.

However, if you have fallen into one of these common fish tank pitch falls, then you may see some of your fish gasping at the surface of the water, in an effort to get some much-needed oxygen through their gills.

This red flag should set all of your alarm bells ringing. 

We have written this informative article so that you are aware of the signs of having low oxygen levels in your fish tank, as well as what you can do to correct the issue, both in the short term and in the long term.

Read on to learn more about maintaining adequate O2 levels in your tank. 

Some Symptoms of Low Oxygen 

Unfortunately for aquarium lovers, the signs of a tank with low oxygen are quite covert, hard to spot, and can go undiscovered until it has reached a critical state.

Unless you want to test the water for dissolved oxygen, you will have to rely on your fishes’ behavior as your indicator of oxygen levels – in particular, low oxygen levels. 

Initially, in the early stages of a tank that has low oxygen levels, your fish will react to the environmental change by moving less, becoming a little sluggish, and even lethargic.

Look out for your fish swimming around less, or just more slowly, as well as eating less.

This happens because oxygen is a key component for metabolic reactions (which give us energy for bodily processes, like movement and digestion). 

As the oxygen levels dip even lower, the fish may start to look labored when they try to breathe, and their gills might be moving more rapidly in an effort to glean more oxygen from the water, by passing a larger volume of water over their gills.

In the later stages of a low oxygen tank, fish will begin to gasp at the water’s surface (though do bear in mind that the gasping looks a lot like fish feeding, and there are some varieties of fish that do take air in at the surface of the tank).

When fish rise to the surface of a low oxygen tank, they will gasp repeatedly for air, often with their mouth wide open, and are sucking in the very top layer of water, which is usually more oxygen rich, as O2 had diffused into the water from the air.  

Some Emergency Steps To Immediately Take

Fish that are gasping at the surface need immediate help.

Even if only one fish is gasping, then the problem is critical, and needs to be treated immediately.

Typically, it is emblematic of a deeper issue with your tank, which will only get worse.

Even fish who aren’t gasping at the surface will still be severely weakened by the low oxygen levels.

A larger water change may solve the issue initially, or at least buy you some more time to find a more permanent solution.

In this kind of situation, we suggest that you change up to as much as 50 % of the water.

We also recommend that you take action by adding a power head or other aeration device could also help on a temporary basis.

Adding an aeration device will improve the oxygen exchange and general movement of the water.

After taking these emergency steps, keep an eye on the fish for any further changes in behavior.

If the fish continue to act weakly, or appear to be struggling for breath, then you should seek professional assistance.

If you decide to add an aeration device, make sure you choose one that is appropriate for the size of your tank.

A small tank will require a smaller diameter, while a large tank will require a larger diameter.

The most common types of aerators are:

Power Heads

These are the most popular type of aerator.

They use a pump to force air through a tube that runs down the side of the tank.

You can purchase them pre-programmed to run continuously, or have them run intermittently.

Some models include timers so that you can set them to turn on and off automatically.

Bubble Nets

These are another option for aerating tanks.

They work by forcing bubbles through a mesh screen that covers the entire bottom of the tank.

The bubbles rise up through the water column and provide oxygen to the fish.

This method works best for tanks with a relatively high water level.

It does not work well for tanks with a low water level because the bubbles tend to rise straight up out of the water rather than dispersing throughout the tank. 

If the issues persist, then you need to identify the root cause of the problem, and then remedy it. Read on to find out more. 

Causes of Low Oxygen Levels In Your Tank

Overcrowding is the #1 reason for low oxygen in your tank.

Other factors rarely cause deaths by themselves if the aquarium isn’t also overcrowded.

You need to reduce the amount of fish in your aquarium.

However, there are other factors that are important if you have a low O2 level in your tank.

These include: 

• Overcrowding causes an elevation in water temperature. 
• A lack of movement in the water/stagnant water. 
• Accumulation of excess waste. 
• Low lighting (when live plants are involved). 
• Use of certain chemicals.  

High Water Temperature 

Higher temperature water holds less oxygen than cooler water.

Lowering the water temperature helps to introduce fresh oxygen into the aquarium.

De-chlorinated water is safer for tropical fish when in the 65 to 70 degrees Fahrenheit.

Partial water changes with warm water (65-70 degrees) are safe for most tropical fish.

Fish need to stay within their normal temperature range.

Air blowing across the surface of the water helps to cool the water.

Ice cubes placed in a zip close bag can be used to drop the water temperature – but you have to be very careful about not lowering the temperature of the water too much! 

Water Movement 

Stagnant water will have low oxygen levels, and can cause fish to become stressed and eventually die of suffocation.

Moving water around helps increase oxygen levels.

A well-designed filtration system increases oxygen levels by moving water around.

Water moving around helps oxygenate the water.

Adding more filters, replacing them, or adding other equipment will help.

A fountain works great. Putting a spray bar on the outlets of the filters will also help.

Using air stones/bubblers will work too, to increase water circulation and water flow. 

Excessive Waste 

Overstocking causes low oxygen levels in your water, as more fish results in more waste.

This can then result in clogged filters, the growth of algae, and lower water quality, all of which can cause a decrease in water oxygen levels.

Additionally, bacteria that work to breakdown waste in the aquarium gravel will use up a lot of the oxygen that is in the tank.

If you think this has been the root cause of your tank’s low oxygen levels, then you need to thoroughly clean your tank, to remove debris.

Then, maintain a good level of upkeep so that the issue does not reoccur.  

Live Plants 

Although not a frequent issue, plants can sometimes cause oxygen level related problems for your fish.

This is because plants need light to grow.

All plants use CO2 and release O2.

However, if the aquarium is dark, the reverse occurs and the plant consumes O2.

The obvious solution to these issues is increased lighting. 

Final Thoughts 

In conclusion, it is important to remember that although overcrowding is often the main culprit behind low oxygen levels, there are many other contributing factors.

It is best to take care of these other factors before tackling the issue of overcrowding.