Does aquaponics need fertilizer?

One of the strengths of an aquaponics system is it mimics the ecosystem's way of growing fish and plants. The soilless system is a closed system that recirculates water from the fish tanks to the plants' grow beds. For this very reason, plants get their nutrients from the fish's excrements with the help of beneficial bacteria.

Ideally, the aquaponics setups do not need fertilizers since it is a standalone means of food production. But in some cases, aquaponics practitioners add fertilizers to address any nutrient deficiency or hasten the plants' growth cycle.

What nutrients do plants need to grow in aquaponics?

Plants typically require six macronutrients in significant quantities. These are Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulphur (S).

Nitrogen: This element is the building block of all proteins and is required for photosynthesis, cell development, metabolic processes, and chlorophyll synthesis. Although most dissolved nitrogen is in the form of nitrate, plants can also grow on modest amounts of ammonia and free amino acids. Nitrogen is a crucial component in aquaponic nutrition solutions and can be used as a proxy for other nutrients.

Potassium: The next element controls the stomatic opening and is involved in flower and fruit set by acting as a cell-signaling molecule via regulated ion flow through membranes. All plants require potassium, and low quantities of this nutrient can harm them. Sugar production and transport, water intake, disease resistance, and fruit ripening need potassium. Treatment is required for potassium deficit in aquaponic plants.

Magnesium: Plants have plenty of uses for the Magnesium element; it is a key component of chlorophyll, which aids in the absorption of light during photosynthesis. Magnesium is required for phosphate metabolism and works as a phosphorus transporter in plants.

Calcium: Another macronutrient for the plant, Calcium is essential for plant growth. It's crucial for maintaining osmotic pressure (keeping plant cells hydrated) and keeping cell walls intact. Consider it the substance that holds the cell walls together and ensures their structural integrity.

Phosphorus: This is another essential mineral for plant growth. Fortunately, it does not become inadequate in aquaponics systems as frequently as other nutrient shortages. Even if phosphorus is available in your system, it may not be sufficient for some plant stages. Plants require phosphorus during root growth and when they begin to generate blooms and fruit.

Sulfur: Another secondary macronutrient is Sulfur (along with calcium and magnesium). Sulfate (SO42-), a soluble anion, is found in aquaponic systems. Sulfate is directly absorbed by plants and is essential for the formation of several amino acids, proteins, and lipids.

Aquaponics plants also need micronutrients to be healthy and disease-resistant. These micronutrients are Iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), boron (B), and molybdenum (Mo).

Iron: Chloroplasts and electron transport chains both need iron. For optimal photosynthesis, iron is required.

Boron: Boron plays a role in the structure of polysaccharides, glycoproteins, carbohydrate transport, and plant metabolic pathways. Boron is also vital for cell proliferation and water uptake.

Manganese: The micronutrient is required for plant photosynthesis since it is used to catalyze water splitting throughout the process. Reduced plant growth rates, a dull grey look, and yellowing between veins that remain green are all signs of manganese deficiency.

Zinc: It aids the plant's ability to survive low temperatures by assisting in the creation of chlorophyll and certain carbohydrates, as well as the conversion of starches to sugars. Auxins aid in growth control and stem elongation, and zinc is required for their production.

Copper: The element is a micronutrient that is instrumental for plant development and growth. It aids in developing lignin in the cell wall and functions as a catalyst in photosynthesis and respiration.

When should I add fertilizers to aquaponics?

Your plant will give you signs that they need fertilizer for additional nutrients. Here are some of the symptoms of various nutrient deficiencies to watch out for:

Signs of Phosphorus Deficiency

  1. Leaves that are brown or purple, bronze, or red.
  2. Stunted leaves with stunted development and undeveloped leaf surfaces
  3. A delay in forming new roots, making water and nutrient uptake difficult.
  4. Leaves might acquire brown patches and necrosis if not handled.

Signs of Iron Deficiency

  1. Your plants' leaves become yellow.
  2. On immature leaves, you can find specific spots.

Signs of Calcium Deficiency

  1. There is a presence of necrosis which refers to black, dead areas of the young plant tissue.
  2. Slight chlorosis to brown or black blistering will be visible on young leaf tips.
  3. Fresh leaves are twisted and have hooked tips and irregular forms.

Signs of Potassium Deficiency

Interveinal chlorosis and spots or blistering appear on the older leaves of the plants, progressing to the younger leaves as the deficit worsens.

How can I add nutrients to my aquaponics system?

The answer to this question depends on the nutrient deficiency you seek to address.


A spray is the most efficient technique to treat calcium insufficiency. Combine some calcium chloride with some water. Four tablespoons per gallon of water is an excellent beginning point. If necessary, you can always raise the dose.

Spray once a week after that.

You can also add some clam bones to your fish tank to improve the calcium and phosphorus supplies.


This mineral is also necessary for optimal plant growth. You'll need to add it in a form that your plants can easily absorb to ensure that they get the most benefit.

Rock phosphate is one of the most frequent and straightforward alternatives. This should be available at your neighborhood garden center.

The supplement can be applied straight to your plant beds, where it will be absorbed practically instantaneously by the roots. Ideally, shield the grow bed from direct sunshine to prevent it from dissolving before the plant can use it.


You will need to use an iron source that the plant can absorb. This necessitates chelated iron, the best of which is Fe-DTPA. If your pH is 7.5 or lower, which should be for healthy plants, this will work.

Aim for a concentration of 2 mg/liter. Calculate the size of your water tank and add the appropriate amount of iron every 3 to 4 weeks.


Potassium can be added to your aquaponics system in two different ways:

1. Spray

Apply potassium chloride to the plants with a spray bottle. You'll need to repeat this technique at least once a week.

2. Additive to Food

Another option is to use kelp meal concentrate to add potassium to the meals. Potassium sulfate or potassium hydroxide are two other choices.

Potassium interacts with calcium and magnesium, lowering the quantity of potassium accessible to your plants. Potassium, unfortunately, comes with a drawback. Your plants may not always have access to the potassium you add.

To ensure that the potassium you provide is used correctly, you should monitor your calcium and magnesium levels and make sure they are balanced.

Should I add more fish to my aquaponics system if my plants lack nutrients?

Many growers believe that when your growth is suffering from any nutrient deficiency, the next thing to do is increase the number of your fish. However, this practice is not always the case because some deficiencies can be solved by giving your plants certain organic mixtures.

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