Look at Aquaponic Macro & Micro nutrients

When I first heard how aquaponics used fish waste to provide nutrients to plants, one of my first questions was how does it work? What are the processes at work that allow this relationship to flourish on both sides? I understood the general theory. The fish eat, the fish produce waste from their food, the waste fills the water with nutrients, and the nutrients are consumed by plants via roots. The process overall is simple. However, there’s more going on here and that’s where things get interesting.

Just like animals, different species of plants have varying adaptations and unique physical structures. Because of this, every plant will have its own needs as far as concentrations and ratios of different nutrients. That being said, most plants require combinations of the same basic macronutrients and micronutrients, macronutrients being nutrients required at higher concentrations and micronutrients only required in trace amounts. Macronutrients make up the bulk of plant requirements so I’ll focus on those, made up of:

  • Hydrogen
  • Oxygen
  • Nitrogen
  • Phosphorus
  • Potassium
  • Sulfur
  • Calcium
  • Carbon

Aquaponics Nitrogen Cycle


In traditional farming, the most supplemented nutrients via fertilizers are nitrogen, phosphorus, and potassium, or NPK as the ratio of concentrations is labelled in fertilizer solutions. These are the primary macronutrients and the most important in plant growth.

Because the main source of nutrients in aquaponics is fish waste, it’s important to understand how fish produce the waste. It seems obvious that the nutrients are provided by the fish feed and the solid waste associated with digestion. But fish poop is not the only form of waste and it may not even be the most important. Freshwater fish secrete ammonia (NH3), in urea as a waste product, which is absolutely vital to the process.

Ammonia is not what plants consume directly and because Ammonia can diffuse back into the fish, it is highly toxic at high concentrations. A conversion is required and that’s where the third player in the aquaponics game comes into the picture. Nitrifying bacteria are bacteria that convert Ammonia (NH3) into nitrite (NO2), and then to nitrate (NO3). These microbes that carry out the process of nitrification are what keep the system running smoothly. Without them, Ammonia would build up in the solution, nitrates would not be present to feed the plants, and both parties would die. Thankfully these little bugs are found naturally in water.

Thanks to fish urine and bacteria, the N of NPK is taken care of with little effort. However, it is important that oxygen levels in the solution are at adequate levels. In the absence of oxygen, denitrifying bacteria take over and the nitrogen in the system is lost to the atmosphere before it can reach the plant roots. This can be achieved through various forms of air pumps and simply making sure that the system has a continuous flow of running water as it moves from tank to tank.

Most other macronutrients are readily available as well. Oxygen and carbon are pulled from the air and hydrogen is in the water. Phosphorus and Potassium, making up the P and K of the NPK ratio, are slightly more complicated. They’re found naturally in the system however not in large amounts. Because of this, greens such as lettuce, basil, and other leafy crops tend to be favored in aquaponics growth. Plants like tomatoes and cucumbers that require large concentrations of phosphorus in order to form reproductive structures like flowers and fruits may need nutrient supplementation in some systems. There has been success growing all kinds of plants using aquaponics, and this remarkable process is by no means limited to greens.


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