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An aquaponics system can be considered functional once nutrient cycling is established, and there are no signs of plant nutrient deficiencies and fish stress. One of the factors that have a significant impact on system cycling is the presence of nitrates. Nitrate is a non-toxic form of nitrogen that is used by plants in building cells. However, high nitrate concentrations can lead to uncontrolled vegetative growth and nitrate accumulation in plant leaves that can be dangerous to human health. The grower must know the best nitrate level for aquaponics to avoid these problems.
According to the Food and Agriculture Organization of the United Nations (FAO), the recommended nitrate level for aquaponics is 5-150 mg per liter or 150 ppm. This is in conjunction with many available anecdotal and research-based literature on nitrates stating that for optimum fish and plant health, 20 to 80 ppm or less is needed.
In this article, we will further discuss the importance of nitrates in aquaponics, the nitrification process, the ideal nitrate level, and how to monitor and adjust nitrate levels.
The role of nitrates in aquaponics
A balance between the biomass of fish and the number of plants is necessary for the production of enough nitrates that are needed in aquaponics. If the number of plants is relatively higher and not proportional to the number of fish, excessive nitrate build-up will affect plant health.
The nitrogen cycle and nitrification process
The nitrogen cycle is an essential biological process in aquaponics systems since plants need nitrates for development and structure. Aquaponics fish produce waste in the form of ammonia that goes through two processes under this cycle to become useful nitrates. Here is a detailed step-by-step explanation on how nitrates are produced:
- The first process in the nitrogen cycle begins when the fish in the tanks excretes waste in the form of ammonia, which is toxic to both plants and fish.
- Ammonia is converted into nitrite through nitrifying bacteria or microbes present in the biofilter of the system. The common bacterium used in this process is called Nitrosomonas.
- Since nitrites are still very toxic, they need to be converted into nitrates; thus, the second process of nitrogen cycle called nitrification. Nitrites are metabolized by another form of bacteria named Nitrobacter to become nitrates.
Ideal nitrate level for aquaponics
Even though nitrates are essential for the aquaponics systems to remain self-sufficient, an excess in its production means that there is an imbalance in the system. If the plants in the grow beds cannot take up all the nitrates because the fish biomass is higher, the remaining nitrates will become dangerous dissolved waste. It is for this reason why identifying the best nitrate level for aquaponics is crucial.
According to FAO, the most recommended nitrate level in aquaponics is between 5 to 150 mg per liter or 150 ppm. Although some fish can tolerate higher levels such as 300 to 400 mg, it would still be better to follow the standard level to avoid hazardous concentrations of nitrates in plant leaves. Most literature on this subject also suggests that 20 to 80 ppm are suitable for higher yield.
Monitoring and adjusting aquaponics nitrate levels
To monitor the nitrate level of an aquaponics system, growers can use six-in-one test strips available in local aquaponics stores and Amazon. This test strip can measure the nitrate level of the water and the level of nitrite, chlorine, alkalinity, pH, and water hardness. Monitoring should be done every two to three days.
In cases of too little or excessive nitrate level in the system, there are several methods that practitioners can do to fix it. If the nitrates are low despite having completed the nitrogen cycle, adding fish or bacteria to the system may facilitate more nitrate build up. If the nitrate level is high, adding more plants, removing fish, and changing some of the water will help balance it.
Nitrates are one of the most critical elements of nutrient cycling in an aquaponics system because it serves as the primary nutrient source of plants. Converting toxic ammonia from fish waste into useful nitrates is done through the nitrification process, which involves certain types of bacteria.
The best nitrate level for aquaponics is 5-150 mg per liter or 150 ppm. This can be monitored using a strip test available from local and online stores. If the level is too high or too low, practitioners can use several methods to balance the system.