Plants - Nutrient Deficiencies

Having an aquaponics system setup does not guarantee that your system will thrive all the times with bountiful harvest. When we grow food in an aquaponics system, the diversity of minerals available to the plants is limited to the elements present in the system. We generally add minerals and chelated iron on top of the daily fish food and it works very well for most crop.

Nutrient deficiencies can become a big problem in your system, affecting plant growth and potentially ruining your harvest. Aquaponics nutrients deficiencies occur when various nutrients are not readily available in the water or fish waste used to feed the plants. This is one of the most common problems in aquaponics and can affect growth and make plants more susceptible to insects and diseases. The first step in preventing or treating aquaponics nutrient deficiencies is recognizing you have a problem and identifying which nutrient your plants need.

A simple key for diagnosing common nutrient deficiencies in aquaponic system.

Step 1: Is your plant Chlorotic? (Is there yellowing of the leaves?)

If yes, see 1a.

If no, go to Step 2

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Step 1a Iron Deficiency

  • Is the yellowing only between the veins, with the veins remaining green?
  • Is the young growth most a­ffected?

If yes, then you most likely have an Iron deficiency.

If no, go to 1b.

How to treat:

Add chelated iron to your system- there are many types out there, but FeEDDHA and FeDTPA are the best types of chelated iron. (FeEDDHA will turn your water red though.) There is quite a bit of math involved in determining how much to add, because different chelated iron types have different purities. Basically, you want to add 2 mg of pure iron per liter of system volume every 4 weeks

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Step 1b Nitrogen Deficiency

  • Is the yellowing across the entire leaf (veins included)?
  • Does the old growth appear to be more a­ffected than the young growth?

If yes then you likely have a Nitrogen deficiency.

If no, go to 1c.

How to treat:

You should know that this is a possibility if you haven’t been feeding much, have too much vegetation to fish, or have been measuring low nitrate levels in your system. Switch to a higher protein feed and feed more often to correct. If this doesn’t correct, remove some plants and look for straw, wood or another high carbon substance in your system that could be consuming nitrogen in decomposition.

Remove all wood, straw, etc. Low temperatures can also depress feeding and lead to nitrogen deficiency.

Picture source from: True Aquaponics Store
Picture source from:

Step 1c Potassium Deficiency

  • Is the yellowing primarily between the leaf veins, but the old growth is most affected?
  • Are the plant leaves cupping, developing brown spots, or dry and dead edges?
  • Are the roots not developing? Are there signs of stunted root growth?
  • Is there some chlorosis or dead fringes around the edges of the older leaves?

If yes, then you likely have a Potassium deficiency.

If no, see 1d. (If old growth is falling)

How to treat:

In systems with low pH, add potassium hydroxide (caustic lye) to raise pH and supplement potassium. In systems with neutral or high pH, add kelp meal concentrate (0-0-10) or potassium sulfate (0-0-50) in very low quantities.

Picture source from: True Aquaponics Store
Picture source from:

Step 1d Magnesium Deficiency

  • Is the yellowing primarily between leaf veins, but the chlorosis is concentrated in older leaves, with the most a­ffected leaves falling off­ (old chlorotic leaves falling off­)?
  • If there are dead fringes along the leaf edges or dead, brown spots on the leaves and the old, chlorotic leaves fall off­, then you likely have a Magnesium deficiency.

How to treat:

In systems with low pH, adding dolomitic lime can help, as well as hydrated lime. In all systems, Epsom salts (magnesium sulfate) can be added in small quantities to supplement magnesium.

Picture source from:
Picture source from:

Step 2 Calcium Deficiency

  • Are there necrotic spots (dead, brown spots) on the leaves or stems of the young, rapidly growing parts of the plant?
  • Are there brown dead spots on the fruit (especially on the blossom end)?

If so, you likely have a Calcium deficiency.

If no, then you may have another nutrient deficiency, but it is not as likely as other variables, including problems with temperature, pests, or cultural methods.

How to treat:

Most systems have plenty of calcium because it’s common in the water. However, if there’s too much potassium in the system, your plants might show a calcium deficiency. To correct in low pH systems, reduce the amount of potassium you are supplementing and add hydrated lime to the system in small quantities. In neutral or high pH systems, the best way to supplement calcium is with small amounts of calcium chloride applied through foliar.

Remember that correcting deficiencies takes time...

often 2-4 weeks, so add small amounts and wait to see the results. Adding too much of any of these substances can sometimes cause bigger problems than a nutrient deficiency! The amounts of these supplements that you add will vary based on system volume and the severity of the deficiency.

Reference: Bright Agrotech


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