Aquaponics may seem like a stand-alone system, the fish provides nutrients or fertilizer for the plants from their waste, so you don’t have to intervene. Aquaponics systems in fact don’t create the perfect environment for overall plant growth.
Additional nutrients such as Potassium (k) and Phosphorous (P) should be added to Aquaponics systems because they are not produced by the fishes in the tank. By testing the water and monitoring plant deficiencies, you would know which of these fertilizers needs to be added to the system.
In aquaponic systems, the waste from the fish is converted to nutrients for the plants. These Nutrients exist in the forms of Nitrogen such as Nitrates. Nitrates are responsible for plant growth and the production of flowers and leaves.
See our complete guide on aquaponics and what you need to know to run a successful system.
Plants as we know require Macronutrients such as Nitrogen, Phosphorus, and Potassium (NPK) as well as other micronutrients. So how do the plants get these other nutrients if it’s not produced by the fishes?
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What Additional Nutrients is Required Aquaponics?
Adding Fertilizer to aquaponics systems requires monitoring the plants for deficiencies.
Also, the type of fishes in the system and the food you are feeding also plays a role in the nutrients that are available for the plants.
Aquaponic plants require a ratio of Nitrogen to Phosphorous to Potassium (N:P:K) and other trace nutrients such as boron, copper, chloride, zinc, magnesium, calcium, iron, and manganese. All these nutrients play an integral part in proper plant growth.
Luckily most trace nutrients are provided by the food which are being fed to the fishes. So take a look at the ingredients in your fish food and you will have an idea of what is also being provided for the plants.
So lets deal with the Macro or larger nutrients, (N,P,K)
We know that plants in the aquaponic system are already provided with copious amounts of Nitrogen from the breakdown of waste by the bacteria to produce Nitrates. The form of Nitrogen (N) that plants love!
But what if the system is low in Nitrogen?
Nitrogen deficiency symptoms?include poor plant?growth, and leaves become pale green or yellow because they are unable to make sufficient chlorophyll.
This can be easily corrected by adding more fish to the system.
Potassium deficiency symptoms in plants include brown scorching and curling of leaf tips as well as chlorosis (yellowing) between leaf veins.
Potassium can be added to aquaponics systems by either directly spraying potassium onto the leaves of the plant which has to be done periodically.
Another way to add potassium to the system is by adding over-ripened or dark to black banana peels directly into the biofilter. Kelp meal concentrate also does a good job. This would create a slow release of potassium into system and would prevent shocking the plants.
Phosphorous deficiency in plants will show stunted growth, darkening of the leaves near the base of the plant, and a purple or reddish color.
Phosphorous can be added to the system by using chlorine-free super triple phosphate or rock phosphate in a quantity of 20 to 40 ppm or parts per million in your system for fruiting plants.
I have made a table that would make it easy to identify the deficiencies and how to correct them.
| Deficiency | Symptoms | Correction |
|---|---|---|
| Nitrogen | Stunted Growth, Pale color, Light green yellowish leaves | Add more fishes to the system |
| Phosphorous | Stunted growth, darkening of the leaves | Add super triple phosphate or rock phosphate |
| Potassium | Brown scorching and curling of leaf tips | add Kelp meal or old banana peels to biofilter |
| Magnesium | Paleness from leaf edges. Edges have cup shapes folds | Use leaf spray, such as Epsom salts |
| Iron | Leaves are pale, No spots, major veins Green | Add Fe-DTPA soluble chelated Iron |
| Calcium | Plant dark green, Drying starts from the tips, Tender leaves pale | Spray calcium chloride onto leaves |
| Boron | discoloration of leaf buds. breaking and dropping of buds | found in trace amounts in fish food |
| Copper | Pale pink between the veins. wilt and Drop. | found in trace amounts in fish food |
| Zinc | Leaves pale, dark spots on leaf edges | found in trace amounts in fish food |
| Molybdenum | spots on whole leaf except veins. Leaves light green or yellow | found in trace amounts in fish food |
| Sulfur | Leaves light green, veins pale green | found in trace amounts in fish food |
| Manganese | Leaves pale in color, veins dark green | found in trace amounts in fish food |
What Affects the Availability of Nutrients
Aquaponics systems require routine water testing in order to maintain the right balance of nutrients available for optimal plant growth.
Water in aquaponic systems is tested for pH, electrical conductivity (EC), and temperature.
Temperature Control – Hight temperatures can cause the bacteria which convert the ammonia into Nitrates for plants. When the ammonia concentration builds it would cause the plants and fishes to eventually die.
pH control is also critical since it would affect the fish’s stress levels and can eventually cause them to die. It also affects how well the plants absorb the available nutrients.
Electronic conductivity (EC), reduces the quality of the crops. It gives an idea of how much available circulating nutrient ions are available for the plants.
These three method of testing is commonly used in aquaponic systems and give a fair indication of the water quality and the available nutrients in the water.
Additionally,
The nitrification process in an aquaponics system is pH lowering by nature, because of this you may need to add both hydrated lime (calcium) and potassium at the same time to both controls the pH and maintain the available potassium in the system.
The hydrated lime would ten to suck up the available potassium in the system, making it unavailable for the plants and hence causing a potassium deficiency. To counteract this you would have to add Potassium into the system.
What Fertilizers are safe to add?
From the table above we can derive the fertilizers or nutrients which are safe to add to aquaponic systems.
| Deficiency | Safe to Use Fertilizers in Aquaponics |
|---|---|
| Nitrogen | Add more fish to the system |
| Phosphorus | Add super triple phosphate or rock phosphate |
| Potassium | Add Kelp meal or old banana peels to the biofilter |
| Magnesium | Use leaf spray, such as Epsom salts |
| Iron | Add Fe-DTPA soluble chelated Iron |
| Calcium | Spray calcium chloride onto leaves |
How do you make aquaponic fertilizer?
Most fertilizers for aquaponics can be found at the plant shop but some can be made at home such as.
- Potassium – use old banana peels or kelp
- Magnesium – Use Epsom salt available at any pharmacy
Furthermore, aquaponics?can rely on?compost tea?for any nutrient supplementation. Compost tea can be made by using a porous bag, and placing organic materials such as banana peels, cucumber peels, carrot peels, and other chopped vegetables.
The bag is then placed into the Biofilter with adequate aeration. The aeration or air bubbles promote bacteria to thrive and break down the copped vegetables within the bag causing them to release helpful nutrients for plants to grow.
When to use fertilizers on plants?
Fertilizers should be added during early mornings between 6 to 8 am and late evenings between 5 and 6 pm.
This is because, during the heat of the day, plants are at their highest level of stress during the mid-day sun. Stress prevents the plants from absorbing the fertilizers through their leaves.
The ambient temperature is much cooler during early mornings and late evenings. The plants are more relaxed and are able to absorb the nutrients through their leaves.
