What nutrients should I add to aquaponics (Fertiliser & nutrient deficiencies)

Does aquaponics need fertiliser and do I need to add nutrients?

Most of the nutrients the plants get in an aquaponics system are obtained from a by-product of the fishes digestive system, i.e. faeces. But sometimes certain nutrients are missing and need to be added. But what nutrients or fertiliser should I add to aquaponics? Let’s take a look…

What nutrients should I add to aquaponics - Nutrient deficiencies

What nutrients or fertiliser should I add to aquaponics in 15 seconds…

Aquaponic plants get most of their nutrients and minerals they need from nutrient-rich water. This natural fertiliser rich water comes from raising fish which provide these nutrients. But occasionally an aquaponic system benefits from the addition of certain nutrients and organisms. Nutrient supplements for aquaponics include chelated iron, vegan plant food like Bio Thrive, organic calcium and magnesium additive, plus beneficial bacteria supplements for aquaponics. With the key focus on the supplements needing to be organic.


Where do the nutrients for the plants come from in an aquaponic system?

You may be wondering where do the nutrients for the plants come from in an aquaponic system. In an aquaponics system the main nutrients needed by the plants originates from a by-product of the fishes digestive system. Which is fish faeces. The fish faeces begin the nitrogen cycle.

You feed the fish; the fish digest the food; then as part of this digestive process they produce waste matter, or faeces. It is this waste matter that decays and produces ammonia. Which is then converted to essential nitrates and other minerals by nitrifying bacteria.

In addition to the excreted fish waste there will inevitably be an element of uneaten food too. This uneaten fish food will also decay. As a part of the decaying process this creates ammonia. This ammonia will feed the bacteria and will also create additional nitrates for the plants.

More Reading: How to lower ammonia levels in fish tank naturally aquaponics

What nutrients should I add to aquaponics and does aquaponics need fertiliser?

Whenever you add anything to an aquaponics system, there are three main considerations to take account of.

These considerations are:

  1. Will the additive enhance the plant or vegetable growth?
  2. Will the additive or fertiliser be harmful to the fish.
  3. Is the additive or fertiliser considered organic and will it affect whether the vegetables and/or fish are still considered organic.

More Reading: Is aquaponics considered organic? (Organic in UK, USA, EU & Canada?)

What nutrients and minerals are required by plants to grow?

The nutrients required by plants to grow healthily are split between non-mineral nutrients and mineral nutrients. But one thing to learn as a beginner aquaponics gardener is how to spot which deficiency your plants have. Plus how the deficiency will manifest in your plants.

Only then will you be able to work out what nutrient is missing. Plus then be able to decide on what natural fertilisers need to be added in order to rectify the deficiency (Natural fertilisers being the operative word to keep things organic).

Non-mineral vs mineral nutrients in aquaponics

Nutrients in an aquaponics system first include non-mineral nutrients. The non-mineral nutrients include oxygen, hydrogen and carbon.

You then have the mineral nutrients. These mineral nutrients include the NPK group of minerals.

NPK minerals needed for plants in aquaponics

The NPK minerals are nitrogen, potassium and phosphorus. These NPK minerals are the primary nutrients needed by plants. Nitrogen is obtained from nitrates, which are derived from the most important process in aquaponics, which is the nitrifying process.

But if you decide you need to add mineral supplements, it’s important to remember that you need to select the right NPK minerals. This way you keep your aquaponics produce organic. But also you’ll not kill your aquaponic fish either by adding the wrong type of fertiliser.

In addition to these primary nutrients, there are also secondary nutrients. These include three key minerals, which are calcium, magnesium and sulphur.

But then there are micro mineral nutrients like iron, copper and zinc. But see the nutrients table below for the rest of these micro nutrients required by plants.

What nutrients should I add to aquaponics table

NutrientTypeSourceNeeds
Adding
Oxygen (O)Non-mineralWater in the aquaponics system.No
Hydrogen (H)Non-mineralWater in the aquaponics system.No
Carbon (C)Non-mineralCarbon dioxide during photosynthesis.No
Nitrogen (N)Mineral - Primary macroNitrates which are formed from the nitrifying process that bacteria convert from fish waste.No
Potassium (K)Mineral - Primary macroPotassium is introduced to your system in the form of fish feed. This is provided as part of the cycling process.Potassium is part of the NPK needed for plants to grow. It's often deficient in aquaponic plants so supplements like potassium hydroxide or kelp meal concentrate will help. But make sure the additive is organic approved.
Phosphorus (P)Mineral - Primary macroBackground levels of phosphorus are normally adequate for typical plant growth and development. But when plants are flowering, set to set fruit or produce vegetables, then more phosphorus is needed.The best way to cheaply supplement phosphate is to use natural rock phosphate. But be aware that additional phosphorus can cause algae blooms in unshaded systems.
Calcium (Ca)Mineral - Secondary macro nutrientPlants can get most of the calcium they need from the water in your aquaponics system.Calcium can be supplemented in your aquaponics system using hydrated lime, which supplements both calcium and magnesium (see below). Or use chelated calcium or calcium carbonate and organic calcium supplement. Alternatively use calcium chloride foliar application.
Magnesium (Mg)Mineral - Secondary macro nutrientPlants can get most of the Magnesium they need from the water in your aquaponics system.If magnesium is low you can add hydrated lime, Epsom salt or soluble kelp concentrate.
Sulphur (S)Mineral - Secondary macro nutrientMostly present.Not normally.
Iron (Fe)Mineral - Micro-nutrientsTrace elements are present.Sometimes needs to be supplemented using Iron chelate.
Copper (Cu)Mineral - Micro-nutrientsTrace elements are present.Not normally.
Zinc (Zn)Mineral - Micro-nutrientsTrace elements are present.Not normally.
Manganese (Mn)Mineral - Micro-nutrientsTrace elements are present.Not normally.
Boron (B)Mineral - Micro-nutrientsTrace elements are present.Not normally.
Molybdenum (Mo)Mineral - Micro-nutrientsTrace elements are present.In plant growth, it helps in the nitrogen, oxygen and sulphur cycles.
Chlorine (Cl)Mineral - Micro-nutrientsTrace elements are present.Not normally.
Nickel (Ni)Mineral - Micro-nutrientsTrace elements are present.Not normally.

Beneficial bacteria in aquaponics

In addition to supplementing mineral and non-mineral nutrients, you may also add beneficial bacteria to your aquaponics system too. The type of supplement you need to add should contain concentrated nitrosomonas and nitrobacter nitrifying bacteria cultures.

Adding beneficial bacteria in this way will encourage your aquaponics system to begin cycling. Which means the ammonia, which is generated from the decaying fish and food waste, gets converted to nitrates more quickly.

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Happy DIY aquaponics.

What nutrients should I add to aquaponics (Fertiliser & nutrient deficiencies)

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