Signs Of Low Oxygen In an Aquarium

Signs Of Low Oxygen In An Aquarium

Though rare in occurrence in well-maintained tanks, low oxygen in an aquarium, can be devastating when it strikes! It can, and possibly will wipe out your entire stock in no time at all. It doesn’t come with bells and whistles that will alert you to its approach, it’s far more subtle than that. Rather, it sneaks up on you and leaves you very little time to act.

Signs of low oxygen is an aquarium- A Strong indicator that your oxygen levels are too low in your fish will be your fish are behaving strangely. They maybe gasping at the surface, less active and rapid gill movement. 

What to look out for

It would be very easy to assume that low oxygen in an aquarium can’t happen to you as long as you provide water for your fish. However, this is not the case as, believe it or not, fish do not get their oxygen from the water. Rather, they are provided with oxygen from the same source as us, the air that surrounds us.

It seems strange I know since water contains oxygen in itself. However, that oxygen is teamed with hydrogen from which it cannot be separated. Instead fish use oxygen that is the result of the gas exchange between the air and the water that takes place on the surface. CO2 (carbon dioxide) in the aquarium is swapped for O2 (water) in the air in a continuous trade. Low oxygen levels occur when this gas exchange becomes limited or non-existent.

Causes Of Low Oxygen Levels in an aquarium

There are several reasons why your aquarium may not have the levels of oxygen that it requires. These include:

  • Overstocking your aquarium
  • Raised water temperatures
  • Lack of surface movement
  • Excess waste in the aquarium
  • Low levels of lighting for plants
  • Improper use of chemicals and medications

Overstocking your aquarium – Every fish you add to your aquarium needs oxygen meaning that the more you add the more oxygen is needed. Put simply this means that if you overstock your aquarium, there will not be enough oxygen to go around.

Raised water temperatures – Warm water is not able to hold as much oxygen as cool water. This means that significant rises in temperature in your aquarium will result in lower levels of oxygen. Keeping your aquarium in the shade or switching off heaters when the temperature rises should prevent this.

Lack of surface movement – Surface movement, it has to be said is probably the most important factor in ensuring oxygen levels remain stable. Movement on the surface of the water increases the surface area and in turn, allows more oxygen to dissolve and carbon dioxide to escape. In stagnant, non-moving water, the opposite is true and can cause low oxygen levels.

If you see your fish gasping for air, that’s a sure sign that you have too little oxygen in your aquarium. We have published a great article all about fish that are gasping for air and the affects on low oxygen.

Ways to ensure a good surface movement include:

  • Aquarium bubblers such as air stones which are attached to an air pump via an airline.
  • HOB filters which release filtered water at the surface causing water motion.
  • Powerheads which can be placed throughout an aquarium and also cause water movement.
  • Wavemakers which replicate the waves you would see in the ocean and seas.
  • Spray bars which attach to an external filters outlet pipe. These gently spray water onto the surface of the water causing agitation.

Excess waste in the aquarium – Excess waste, can clog up filters causing a decrease in the dissolving of oxygen. It also lowers the oxygen carrying capacity of the water in general. Good aquarium maintenance solves this problem.

Low levels of lighting for plants – It’s a well-known fact that plants use carbon dioxide and release oxygen into the water. However, in poor/dark lighting conditions this process is reversed and plants use oxygen and release carbon dioxide. Good artificial aquarium lighting will help ensure that this reversal in the process does not happen.

Improper use of chemicals and medications – Certain chemicals, like water conditioner, and medications can have a direct negative impact on the oxygen-carrying ability of water when used in the incorrect amounts. Always ensure you read the label on aquarium products and that you follow instructions carefully.

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Signs That The Level Of Oxygen In Your Aquarium Is Low

Without regularly using a dissolved oxygen level testing kit there is only one indicator that your oxygen levels are too low, and that is the behavior of your fish. This behavior or indicator will, in most cases, follow three stages.

1 First, your fish will begin to be less active. They will swim less, move around, in general, less, and may even begin to eat less. Bear in mind that if you have an aquarium of less than active fish such as plecos, glass catfish, etcetera, this sign may not be the easiest to spot.

2 As the oxygen levels continue to drop your fish will start to show signs of labored breathing. These may include more rapid gill movements as they attempt to get more oxygen through their gills, and occasional swimming to the surface to gasp for air.

Be careful not to confuse this behavior with fish that are feeding, or that surface breathing is normal for. Labyrinth fish such as gouramis and bettas regularly visit the surface for a breath or two before swimming back down into deeper water.

3 Finally, all your fish will congregate at the surface gasping repeatedly for air with wide-open mouths. If you find your fish at this stage, you should take action immediately. A 50% water change is the action advised as the new water will bring in dissolved oxygen that should help your fish survive. Using a top quality filter like an External canister filter will help in two ways. Firstly to remove harmful dirt and debris and lower ammonia and nitrate levels in your aquarium. And secondly, the water that is pumped back into your tank will aerate the water and provide vital oxygen levels to increase. 

You may find that it is just the vast majority of your fish that are gasping at the surface and not all. However, this does not lessen the issue you are facing and you should still take action. The fish not at the surface may simply be a little stronger than the others or do not need as much oxygen in the first place.

Conclusion: Signs of low oxygen in a fish tank

It has to be said that as with any problem you may face in the fish keeping hobby, prevention is always better than cure, and low oxygen levels are no different. Spotting Signs Of Low Oxygen In An Aquarium before it harms your fish is beneficial for all, fish and yourself. But did you know you can also have too much oxygen in an aquarium? No! Then read our article on this topic to find out more. You’ll be very surprised. 

They are also easily avoided by taking just a couple of simple steps. The first is to provide good tank maintenance such as water changes and cleaning, and the second to provide a good surface agitation. Do this, and you will have fish that breathe easy!