What is Dissolved Oxygen in Hydroponics?


To get the best growth from your hydroponic garden, monitoring your system’s DO or dissolved oxygen should be a top priority. When it comes to growing your own food, healthy plants lead to bigger yields and fewer problems with disease and pests.  

Dissolved oxygen (or molecular oxygen) is a form of oxygen naturally found in most water sources and is what plants use to grow. For hydroponics, you’ll want to control the amount of DO in the water you use. Generally, the recommended DO level for hydroponic plants is around 7-10 PPM (parts per million).

When I first started my hydroponic garden I had no idea what dissolved oxygen was. This article is a guide to understanding how much DO your plants will need, how to measure DO and more.

What is Dissolved Oxygen in Hydroponics?

It’s common knowledge that water molecules are made up of hydrogen and oxygen. These atoms are bound together, creating H2O. 

However, you may not know about a different form of oxygen that hangs around between those water molecules called dissolved oxygen (sometimes called molecular oxygen). 

Dissolved oxygen is what plant roots use for growth. As I mentioned, most water sources produce DO. 

However, the amount of DO will vary depending on a few different factors including:

  • Water temperature
  • Pollution levels
  • Water aeration (which is the process of bringing air and water close together to remove dissolved gasses such as carbon monoxide)

DO can even be found in the water you get from your tap. However, tap water only has about 5-7 PPM (or parts per million) at room temperature.

For your hydroponic plants you’ll need water with DO ranging from around 7-10 PPM. The DO content in your water needs to be measured and maintained. This will help reduce many of the common plant problems in hydroponics.

Why Your Plants Need DO

There’s no way around it, if your goal is to get the best yields out of your hydroponic crops, then the water you use to nurture them needs to contain DO.

Plant root systems use oxygen for aerobic respiration — a reaction to glucose and oxygen being transported to the plant’s tiny cells (or mitochondria) — and with a hydroponic system most of the oxygen that is used in root uptake is contained in the nutrient solution.

Plant roots become less permeable, meaning they will take in less water and will no longer be able to properly absorb nutrients if they don’t get enough oxygen.

Toxin build up is also a result of not enough oxygen. If this deprivation of oxygen is allowed to continue, the plants will start to starve due to a lack of nutrition.

Ultimately, pathogens can invade your plants and cause them to die. Aeroponic systems are designed to maximize the amount of oxygen available to the plant roots which increase nutrient uptake.

Tower Garden Aeroponics System

What Effects DO Levels in Water?

There are two primary factors that can have a serious impact on DO levels in your hydroponic system, water purity and water temperature.

Water Purity Effect on Dissolved Oxygen

If you’re thinking of filling your hydroponic system with regular tap water, be sure to let is sit for a few hours and allow the chlorine to evaporate before adding it to the reservoir.

Tap water typically contains other elements such as chlorine that can reduce the amount of oxygen the water can hold. 

The salinity of the water is an additional factor here. The higher the salinity of the water, the less soluble the oxygen will be, which results in lower levels of DO. 

If your water contains contaminants like bacteria, this will also reduce the DO levels made available to plant roots.

For all of the reasons listed above, many (myself included) choose to use water that has been filtered via reverse osmosis. Distilled water is a good alternative as well.

The proper amount of nutrient solids will be added to this water to meet the nutritional needs of the plants.

Water Temperature Effect on Dissolved Oxygen

Another factor to consider is temperature as this can also impact how much dissolved oxygen your water will be able to hold.

The lower the temperature of the water is, the more oxygen it will be able to hold. On the other hand, the higher the temperature, the less DO the water will hold. 

How Much Dissolved Oxygen Do Hydroponic Plants Need?

When it comes to how much dissolved oxygen your plants will need, the answer is 7-10 PPM. Anything less than this can be detrimental to plants and potentially cause plant death. 

With that being said, maintaining this level of dissolved oxygen can be tricky if you aren’t regularly measuring DO levels.

Just like providing the right amount of nutrients to your hydroponic vegetables is important, you’ll need to ensure they are getting the right amount of oxygen as well.

How to Measure DO Levels in a Hydroponic System

The easiest way to measure DO levels in a hydroponic system is by using a dissolved oxygen meter.

Depending on the model, DO meters can use a variety of sensors to measure the amount of gaseous oxygen dissolved in a water sample. These sensors include:

  • Polarographic sensors
  • Galvanic sensors
  • Optical sensors
  • Amperometric sensors

These devices are typically used in aquariums — as DO levels can impact fish too — but can also be used to measure levels in the water you intend to use for your hydroponic plants.

Here are some of my favorite DO meters to use:

1. RCYAGO DO Meter with Electrode Filling Fluid

  • Uses a polarographic sensor to measure DO levels
  • Includes a detachable probe that is easy to replace
  • Backlit digital screen display is easy to read
  • Auto shut-off in 8 minutes to conserve battery life
RCYAGO Dissolved Oxygen Meter with Electrode Filling Fluid
  • Dissolved oxygen meter is a precision instrument for measuring dissolved oxygen and...
  • Dissolved oxygen refers to the concentration of molecular oxygen dissolved in water, generally...
  • Detachable probe, easy to replace, equipped with 6 probe protective covers. The film inside the...

2. Apera Instruments Portable Optical DO Meter Kit

  • Uses an optical probe sensor to measure DO levels
  • Features quick and easy calibration
  • Compensates for salinity, temperature, and air pressure automatically
  • Comes with a complete test kit (including salinity probe, 10 foot optical probe, calibration cap and a durable carrying case
APERA INSTRUMENTS AI485 DO8500 Portable Optical Dissolved Oxygen Meter Kit,...
  • Equipped with state-of-the-art Optical DO sensor: measures dissolved oxygen level in a RELIABLE...
  • Minimal maintenance required. Quick and easy calibration
  • Automatic compensation for salinity, temperature& air pressure

3. Extech Waterproof ExStik II DO Meter

  • Comes with a replaceable membrane cap and optional extension cables
  • Adjustable salinity concentration (from 0 to 50 ppt)
  • Device self calibrates as soon as you power it up
  • Analog paragraph indicates trends
Sale
Extech DO600 Waterproof ExStik II Dissolved Oxygen Meter
  • 0 to 50°C Temperature Range
  • 1.4" D x 6.9" H x 1.6" W
  • 3.8 oz Weight

How to Increase DO Levels For Hydroponics

To increase dissolved oxygen levels, you can use one of the following:

  • Air Stone: this product bubbles air into the water to increase DO levels. You can find air stones online and the best part is they are inexpensive! 
  • Hydrogen Peroxide: you can add hydrogen peroxide to water to increase DO levels as well. Keep in mind, you’ll want to ensure you’re not adding too much as this can be detrimental to your plants.
  • Hydroponic Air Pump: most growers use air pumps in combination with an air stone to regulate and maintain DO levels in their hydroponic systems.

Can You Have Too Much Oxygen in Hydroponics?

While the goal of most hydroponic growers is to maintain and regulate adequate oxygen levels in their hydroponic systems, it is possible to add too much.

When too much oxygen is added to a hydroponic system it could cause root stunting and plant damage, so it’s definitely something you want to avoid. 

Luckily, it’s very difficult to reach excessive oxygen levels — which is typically around 15-16 PPM — by using conventional methods such as air stones and air pumps.

In order to reach levels above 10 PPM, you usually need to use ozone or liquid oxygen. Keep in mind, most growers try to maintain a DO level of 7-10 PPM. 

Final Thoughts

To recap:

  • DO (or dissolved oxygen) is a form of oxygen naturally found in water sources and essential for plant growth in hydroponic systems.
  • Measuring DO levels (using a DO meter) is crucial to maintaining the proper oxygen level in your hydroponic systems and ensuring your crops will thrive.
  • You can increase DO levels using air stones, air pumps, or hydrogen peroxide.
  • Be careful not to reach excessive levels of oxygen in your hydroponic system to avoid root stunting and plant damage.

I hope this article helped you gain a better understanding of DO and hydroponic systems as a whole!

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