Author: Aqua Gardening

Aquaponics Oxygen Levels

Aquaponics Oxygen Levels

Aquaponics and hydroponics plants grow 30% better than soil based - in fact the rule is a 30% increase for plants, 30% faster growth and 30% higher yields. How is this possible? Oxygen is one of the major contributors to this growth.

Methods to Increase Oxygen in the Root Zone

Having oxygen around a plants roots is vital for plant growth. Aquaponics and hydroponics use the following methods to maximise oxygen around the plant roots:

  • Flood and Drain: flooding and draining the water from the grow bed - a cycle of nutrient enriched water, followed by draining to allow air in and around the roots
  • Aeroponics: spraying a fine stream of nutrient and oxygen enriched water onto the plant roots inside a dark tub
  • NFT: short for "Nutrient Film Technique" which provides a constant stream of nutrient rich water in a channel while keeping space free for oxygen absorption between the plant's stem and roots
  • Floating raft: growing plants on a top of a nutrient reservoir and keeping an air space for the roots between the water surface and stem of the plant.

Technically speaking, fish and plants both need a specific amount of oxygen, read on to find out exactly how much.

Oxygen for Fish

Dissolved Oxygen (DO), the volume of oxygen contained in water, is often the critical parameter in the health and well-being of your livestock. In general, most fish species will grow and thrive within a DO range of 5-12 mg/L. However, if levels drop below 4 mg/L fish may swim at the surface, breathe rapidly and reduce their appetite. If low oxygen levels persist, fish become stressed and may begin to die. This series of events can cause a chain reaction in an aquaponics system that could prove detrimental. Oxygen depletion usually occurs in the summer months because warmer water holds less oxygen than cooler water. Higher temperatures also increase the metabolic rate of fish resulting in the need for more oxygen.

Oxygen for Plants

Plant roots require oxygen for aerobic respiration, an essential plant process that releases energy for root growth and nutrient uptake. Injury from low oxygen in the root zone can take several forms and these will differ in severity between plant types. Often the first sign of inadequate oxygen supply to the roots is wilting of the plant under warm conditions and high light levels. Insufficient oxygen reduces the permeability of the roots to water and there will be an accumulation of toxins, so that both water and minerals are not absorbed in sufficient amounts to support plant growth. Plants also show signs of low oxygen by browning and/or dying roots and roots that are slimy to touch. The recommend oxygen level for plants grown in an aquaponic system is 4-12 mg/L. If much algae is growing in the aquaponic system oxygen levels can vary during 24 hours. This is due to algae, like higher plants, respiring 24 hours but only releasing oxygen during daylight hours. This increased Biological Oxygen Demand (BOD) can cause the oxygen level to be at its lowest just before the sun rises. This is the reason why excess algae is not is not favoured in aquaponic systems.

Guide to Matching an Air Pump to your Aquaponics Fish Tank

Air compressors are a method used to raise oxygen levels for your system. The following table shows what size pump is required for different water volumes. The water volume should be calculated from the combination of your fish tank, sump and grow beds.


Water Volume (L) Pump Output (L/hr)
10-100 Aqua One SR2500 150
80-100 Aqua One SR7500 210
200 Otto SA-11000 (Battery Backup) 480*
100-200 Aqua One SR9500 510
350-700 Aqua One SR1200 1900
1000 Hailea ACO 208 2100
2000 Hailea ACO 328 4200
1500 Hailea 12V ACO-003 3300
3000 Hailea 12V ACO-006 6,000

*AC power, DC power: 180L/hr This guide is subject to the number and size of fish per volume of water, different stocking densities can influence the size of the air pump required to maintain adequate oxygen levels.