Diagnosing Potassium Deficiencies in Aquaponics

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Recognizing Potassium Deficiencies

Part #1) Introduction to Potassium

Part #2) Potassium in Your System

Part #3) Diagnosing Potassium Deficiencies in Aquaponics

Part #4) Managing Potassium Deficiencies


Potassium deficiencies can be difficult to diagnose, primarily because they resemble in many aspects, deficiencies in Calcium and Magnesium

There are some distinguishing features however…

How Do I Know It’s A Potassium Problem? *

potassium in aquaponics

Interveinal chlorosis (yellowing leaves) on oregano.

Potassium will typically show up initially as interveinal chlorosis, starting in the older growth.

This is because potassium is mobile in the plant, allowing the plant to move what potassium it has from the old growth to the new, delicate growth.

If the potassium deficiency isn’t initially treated, it will get worse, culminating in browning, drying and death of the edges of the leaves, dead, necrotic spots on the leaves, bronzing and cupping.

Each crop can show slightly different symptoms, and oftentimes, when the deficiency becomes extreme, it becomes impossible to differentiate from calcium deficiency.

One tell-tale sign for many crops in aquaponic systems is the stunting of root growth, meaning that plants show slowed or stunted growth and can be easily pulled from the media.

The root system of pulled plants will be small, often browned, and lack lots of structure.

To help with diagnosis, please download the key that I’ve developed.

It isn’t foolproof, but it can often give you a starting point for diagnosing potassium, calcium, magnesium and iron deficiencies, and help you to see the differences between them.


Find Out How To Manage Deficiencies *

Learn how to manage and treat potassium deficiencies here in the 4th part of this series.

Click here to learn more.


treating potassium deficiencies in aquaponics



  1. so, what is best to add in order to have potassium?

  2. Hi Nate,

    Thank you for the wonderful lecture about potassium. It’s seem very simple and easy to understand the way you explain this thing. . I have one question though, what is the right dosage for potassium sulphate that I need to put in my system? Thank in advance.

    • Hey Lawrence, we typically add potassium sulfate at very low levels. It really depends on the deficiency, but we almost never add more than 1/2 ounce per every 1000 gallons. That’s a low dosage but it’s very concentrated stuff and it’s better to try to correct those deficiencies over a longer period of time rather than over night. Specific dosages can be formulated if you know the actual potassium content of your solution.

      • How often would you add that amount of potassium sulfate?

        • You can start adding 1 tsp per 1000L once a week. If you don’t see any deficiency correction, you can add it with an increased frequency until you see a correction. Just use some caution in this process. Watch your plants, watch your fish and be sure your system isn’t reacting poorly.

          • thanks will give it a go.

  3. Hey Nate, I have a small setup with a 10 gallon fish tank with 4 gold fish and a 10 gallon float table. I’m using this as a practice model for a larger setup that I plan to build. I’m growing mostly lettuce right now and believe they are showing a potassium deficiency. I can’t find potassium hydroxide so I’ve been dissolving granulated potash (0-0-60) at 1 tsp/L and adding about 1 tbsp/week but the deficiency persists. My pH is about 6.8-7.0. Would you suggest upping the concentration of my solution? If so by how much? Are there any other suggestions you would give? Great series BTW, very informative, precise, and to the point. 

  4. Chris/Nate,

    Are you able to provide a source for the kelp meal you use? The entire Internet seems to agree that kelp meal is 0-0-10 and is reasonably priced, but no one offers sources and I have found it nowhere. I find 1-0-2 and 1-1-17 and 1-0-4 and 0-0-18 and they are all very expensive. Even though everyone says kelp meal is 0-0-10 and not expensive, multiple Internet searches have turned up absolutely zero evidence.

    Do you have salt build-up and the resulting problems? NaCl appears to be 6-8% of most kelp meals which seems very high especially if I am using it to supplement K which may be only at 2%(even at K levels of 18%).




  1. Comment on Diagnosing Potassium Deficiencies in... - […] You can start adding 1 tsp per 1000L once a week. If you don’t see any deficiency correction, you …
  2. Potassium in Your Aquaponics System (Part 2) - […] Read part 3 here […]
  3. Potassium in Aquaponics: A Helpful Overview - […] 3. Potassium Deficiencies- Recognizing Them and Why they Occur […]

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