Swirling Oxygen: Is Your Aquaponics System Circulating Properly?

By Shannon McKee
Published: October 28, 2019 | Last updated: April 30, 2021 12:36:56
Key Takeaways

Your crop and fish may be getting by, but are they thriving? If not, you may want to ensure your system is circulating well and dissolved oxygen levels are ideal. Shannon McKee explains what to look for.

There are a lot of different things you can measure in your aquaponics system. The conditions and quality of the water in the system will determine the quality of the crops you’re growing and the health of the fish. If one little thing goes out of whack, your system could be in big trouble to the point where you may have a devastating event on your fish and crops.


You’ve probably tested the temperature, pH, ammonia levels, and other factors in your system. However, have you tested to see if your circulation system is running correctly? The oxygen level in your aquaponics system is probably one of the most important things you should be checking. Poor circulation in your systems means there won’t be adequate levels of dissolved oxygen in the water for the fish and plants.

Signs You Need to Check Your Dissolved Oxygen Levels

The best way to identify how well your circulation system is working is through testing the dissolved oxygen in your system, but there are other clues that can tell you there’s a problem with the amount of oxygen you have. Your fish are the perfect canary in your aquaponic setup, and you’ll probably notice the signs that the fish give off about the oxygen levels before you notice issues with your crops.


Read also: Dissolved Oxygen: The Hidden Necessity

Just like a miner’s canary, the fish can give you clues about the environment you’re growing in. Here’s what to look for in your fish that could signal a problem with your oxygen levels:

  • Poor appetite where they aren’t eating as much as they did previously.
  • Your fish don’t seem to be getting any bigger as their growth has stopped or slowed.
  • You’re dealing with more disease or parasites as your fish can be more susceptible in lower oxygenated water.
  • You may also notice your fish are all swimming right around the inflow pipe trying to get more oxygen in their system.
  • Your fish are gasping at the surface trying to take in more oxygen. This sign is a red alert that your circulation system isn’t providing enough oxygen for your fish and you need to do something fast before you lose them.

When you notice these signals, you’re going to want to start testing your system for problems, with the first tests focusing on the oxygen levels. It’s possible your fish may have been harmed from the period of reduced oxygen, so even after you get this addressed, you will need to continue monitoring them.

There are also some signs your plants’ roots aren’t getting enough oxygen as well. These include root rot where roots are dying off; plant growth can be hindered from a lack of the correct nutrients making it to the plant, and a lack of calcium can occur. Keep in mind that when your plants start to flower and bloom, they need even more dissolved oxygen.


Testing the Dissolved Oxygen

There are two ways you can test your oxygen levels, and each have their own pros and cons.

The first is using a test kit that can help you determine an imprecise, but still helpful number that gives you an idea of the level of your oxygen. This testing kit can be time-consuming to use, but it’s an inexpensive way to check your circulation system.


The other option you have is to invest in a dissolved oxygen meter, also known as a DO meter. This tool is a bit more expensive than the test kits but gives you faster and more precise results when it comes to your oxygen levels.

Dissolved Oxygen Levels

The exact amount of dissolved oxygen you want in your aquaponic system will depend on what fish and the plants you are farming. Some species of fish, such as the black bullhead, and plants, such as taro or lettuce don’t require high levels of dissolved oxygen and can be happy in about 3 mg/liter.

Read also: 3 Aquaponic Stress Factors

However, most of the fish you farm will need at least 4-5 mg/liter with some requiring as high as 8 mg/liter. Trout and salmon are both at the higher end of the scale. Also remember that even though your fish can survive at a lower level, they may not be thriving. If you want them to grow and to breed, a higher oxygen level in your aquaponics system is crucial. Some people believe you can add as much oxygen as you like as long as your fish aren’t being blown out of the water by the amount of aeration added.


There are a few solutions to circulation system issues in your aquaponics system after you’ve checked it for any issues. Problems with your equipment, such as breaks or build-up may mean items need to be repaired or replaced. Once you handle this maintenance, it can be a good idea to check your dissolved oxygen levels again.

Another solution is to add another aeration device in addition to moving some of the water that comes from flooding, and draining your grow beds to the fish tank. You can also make a water feature with a dynamic water flow. This addition is helpful as the cascading water going back into the system will add oxygen to the water.

Remember that heat can reduce the amount of oxygen in the water, so increase your aeration efforts during the hottest months or find ways to cool the water. In addition, you want to make sure you’re not overstocking fish in your system.

A final way to keep your circulation system running smoothly is to ensure you have backup power in case of an outage. A battery backup to your pumps will help to save your fish during the next blackout.

Keeping an eye on your oxygen is just as important as the temperature, nutrient solution, pH, and other factors you test. When it comes to your aquaponic system, it’s vital to ensure your circulation is adequate to keep both your fish and your plants happy and healthy. The key to checking the circulation is testing the dissolved oxygen that’s in the water located in different points in your system and, if something is wrong, adapting the system to fix circulation problems will keep your fish thriving.


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Written by Shannon McKee | Freelance Writer, Gardener

Profile Picture of Shannon McKee

Shannon McKee lives in Ohio and has been a freelance writer for several years now, including on her blog, Nicknamed by loved ones a garden hoarder over the past few years, she grows a wide variety of plants in her urban garden.

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