Adding Fertilizer to Aquaponics System: Should It Be Done?

Aquaponics System

Aquaponics may appear to be a self-contained system because you don’t need to get involved because the fish excrement acts as fertilizer for the plants. In actuality, aquaponics systems don’t produce the ideal environment for total plant growth.

Since the fish in the tank do not manufacture certain nutrients, such as potassium (k) and phosphorus (P), additional nutrients should be provided to aquaponics systems. You would be able to determine which of these fertilizers should be given to the system by analyzing the water and keeping an eye on plant deficiencies.

The excrement from the fish is transformed into nutrients for the plants in aquaponic systems. These nutrients can be found as nitrogen-containing substances called nitrates. Nitrates are essential for plant development, including the growth of leaves and flowers.

See our comprehensive guide on aquaponics to learn all you need to manage a system successfully.

We already know that plants need various micronutrients in addition to macronutrients like nitrogen, phosphorus, and potassium (NPK). If the other nutrients aren’t created by fish, how do the plants obtain them?

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What Additional Nutrients is Required in Aquaponics?

Monitoring the plants for deficiencies is necessary when fertilizer is added to aquaponics systems.

The nutrients that are accessible for the plants also depend on the kind of fish in the system and the food you are feeding them.

Nitrogen, phosphorous, and potassium (N:P:K) ratios are necessary for aquaponic plants, as are other trace nutrients including boron, copper, zinc, magnesium, calcium, iron, and manganese. All of these minerals are essential for healthy plant development.

Fortunately, the majority of trace nutrients are provided by the food that is fed to the fish. So, to get an indication of what is also being provided for the plants, check at the contents in your fish meal.

Let’s now discuss the macronutrients, or bigger nutrients (N,P,K)

We are aware that the abundance of nitrogen supplied to plants in the aquaponic system comes from the bacteria’s decomposition of waste into nitrates. the nitrogen (N) molecule that plants prefer!

But what if the nitrogen level in the system is low?

Poor plant development is one of the signs of a nitrogen deficiency, and the leaves turn pale green or yellow because there is not enough chlorophyll being produced.

Adding extra fish to the system is an easy way to fix this.

The curling and browning of leaf tips, as well as chlorosis (yellowing) between leaf veins, are signs of potassium deficiency in plants.

Aquaponic systems can have potassium supplemented by either directly spraying potassium into the plant’s leaves, which must be done on a regular basis.

Banana peels that are overripe or dark to black can also be placed directly into the biofilter to supply potassium to the system. Additionally, kelp meal concentrate works well. This would prevent stunning the plants and result in a gradual release of potassium into the system.

Plants with a phosphorus deficit will exhibit stunted growth, darkening of the leaves close to the plant’s base, and a purple or reddish hue.

For fruiting plants, phosphorus can be added to the system by utilizing chlorine-free super triple phosphate or rock phosphate in amounts ranging from 20 to 40 ppm, or parts per million.

I created a table that would make it simple to spot the errors and how to fix them.

NitrogenPale tint, stunted growth, and light-green, yellowish leavesExpand the system’s fish population
Phosphorousslow growth and a fading of the leavesAdd rock phosphate or super triple phosphate.
PotassiumThe tips of leaves are becoming brown and curling.add old banana peels or kelp meal to the biofilter
Magnesiummargins of the leaves are paler. Edges are cupped and feature folds.Spritz leaves with anything like Epsom salts.
IronPale leaves with no markings and green major veinsAdd soluble Fe-DTPA chelated iron.
CalciumPlant dark green, tender leaves pale, and drying begins at the tipsCalcium chloride aerosolized onto leaves
Boronleaf buds that are discolored. bud breakage and droppingfound in fish food in trace levels
CopperBetween the veins, pale pink. drop and wiltfound in fish food in trace levels
Zincleaf margins have black dots on pale leaves.found in fish food in trace levels
MolybdenumSpots cover the entire leaf, excluding the veins. Light green or yellow leavesfound in fish food in trace levels
SulfurLight green leaves with pale green veinsfound in fish food in trace levels
ManganesePale leaves with dark green veinsfound in fish food in trace levels

What Affects the Availability of Nutrients

What Affects the Availability of Nutrients

Regular water testing is necessary in aquaponics systems to maintain the ideal ratio of nutrients available for the best plant development.

The pH, EC, and temperature of the water in aquaponic systems are measured.

Controlling the temperature – High temperatures can harm the microorganisms that turn ammonia into nitrates for plants. The plants and fish would eventually perish as the ammonia concentration rose.

The fish’s stress levels would be impacted by pH regulation, which could ultimately lead to their demise. The ability of the plants to absorb the available nutrients is also impacted.

Electronic conductivity (EC) lowers the crops’ quality. It provides a rough estimate of the amount of circulating nutrient ions that are available to the plants.

These three testing techniques are frequently employed in aquaponic systems and provide a reliable indicator of the water quality and nutrients that are present.


Since the nitrification process in an aquaponics system naturally lowers pH, you might need to feed both hydrated lime (calcium) and potassium at the same time to preserve the system’s potassium availability.

The potassium would start to be sucked up by the hydrated lime, rendering it unavailable to the plants and leading to a potassium deficit. You would need to supplement the system with potassium to counteract this.

What Fertilizers are safe to add?

We can determine the fertilizers or nutrients that are safe to apply to aquaponic systems from the table above.

DeficiencySafe Fertilizer Use for Aquaponics
Nitrogenenlarge the fish population
PhosphorusAdd rock phosphate or super triple phosphate.
PotassiumOld banana peels or kelp meal can be added to the biofilter.
MagnesiumSpritz leaves with anything like Epsom salts.
IronAdd soluble Fe-DTPA chelated iron.
CalciumCalcium chloride aerosolized onto leaves

How do you make aquaponic fertilizer?

The majority of fertilizers for aquaponics are available at plant supply stores, although some can be created at home, like.

  • Use kelp or old banana peels for potassium.
  • Use Epsom salt, which is available at any pharmacy, for magnesium.

Additionally, compost tea can be used as a nutrient supplement in aquaponic systems. You can make compost tea by putting organic materials like banana peels, cucumber peels, carrot peels, and other chopped vegetables in a permeable bag.

Following proper aeration, the bag is then inserted into the Biofilter. The aeration or air bubbles encourage microorganisms to flourish and decompose the chopped veggies inside the bag, releasing beneficial nutrients for plant growth.

When to use fertilizers on plants?

Early in the day, between 6 and 8 am, and late in the day, between 5 and 6 pm, are the best times to add fertilizer.

This is due to the fact that plants are most stressed out during the midday sun when it is hot outside. Stress hinders plants’ ability to take up fertilizers through their leaves.

Early mornings and late evenings have substantially colder ambient temperatures. The plants are more at ease and may use their leaves to take up the nutrients.


How do I add magnesium to my aquaponics system?

How do you add minerals to aquaponics?

Does aquaponics need fertilizer?

With aquaponics, you may grow healthy plants without using fertilizer since it mimics the way that the natural balance of nutrients occurs. In an aquaponics system, fish waste found in the water fertilizes the plants, and in exchange, the plants maintain the health of the fish by filtering the water before it is returned to the tank.

What nutrients should I add to aquaponics?

Your Aquaponics system’s most crucial components are nitrogen, phosphorus, potassium, calcium, sulfur, and magnesium. Additionally, trace amounts of boron, copper, chloride, zinc, molybdenum, iron, and manganese are required by your plants.