Magnesium in Aquaponics

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The Importance of Magnesium in Aquaponic Systems

Magnesium is a very important plant nutrient and is up with Potassium when it comes to common plant deficiencies in aquaponic systems.

Magnesium is an important part of enzymes, proteins and the machinery of photosynthesis, and when it’s deficient, it can really impact the productivity of your system.

Magnesium is one of the plant nutrients that interacts with potassium and calcium in “antagonistic” or competitive ways.  To confuse the issue more, magnesium deficiencies can also be difficult to differentiate from deficiencies of these other nutrients!  That’s why it’s important to use a key when you’re first starting to diagnose deficiencies. 

What does a magnesium deficiency look like?

Magnesium deficiency is characterized primarily by interveinal chlorosis (yellowing between leaf veins)  with old growth falling off.  Some plants will show burning along the fringes of the leaves, bronze or brown spots on leaves, and occasionally cupping, but most of the time you’ll just have interveinal chlorosis with old growth falling off the plant.

Treating Magnesium Deficiencies

magnesium in aquaponicsTreating magnesium deficiency requires that you keep potassium and calcium at the correct levels too.  The easiest way to do this is to add all three together.  One way to do this is to use hydrated lime and potassium hydroxide together to raise pH. 

When you add 1 part potassium hydroxide and one part hydrated lime together, you raise the concentrations of potassium, calcium and magnesium together in solution.  As your system matures, you’ll learn that each fish feed has different levels of these nutrients, and different crops consume these nutrients at different rates. 

To correct for these different variables, keep your eyes open for any deficiencies and raise increase the ratio of the nutrient that you believe to be deficient.  

In neutral pH systems, you don’t always want to raise pH.  In these scenarios, we typically recommend weekly doses with soluble kelp concentrate powder to supplement potassium, while adding chelated calcium and magnesium in the form of Epsom salts- which is basically a magnesium sulfate.  In this scenario you must be observant, as any deficiency might creep up and require a modification of the amount that you’re dosing each of these nutrients at each week.  

Check out the video:


More on Magnesium

Magnesium isn’t as much of a concern as potassium but it is still very important, and commonly deficient. 

Use the Bright Agrotech key to diagnose deficiencies and don’t be afraid to ask for more information. 

Good luck and happy growing!

 <<<< Download the key here. 

9 Comments

  1. When giving info on deficiency could you explain what the plant would do if you add too much correction?

    Reply
    • Tom, you can see toxicity with some nutrients as well as deficiency of other compounds if there is too much of one element in your system. However, we don’t usually address this as toxicities are very uncommon compared to deficiencies. If you’re interested in what toxicities look like there’s a lot of info online posted by great university sources. We’ll probably address toxicities at some point, but we have to get through deficiencies first!

      Reply
  2. “When you add 1 part potassium hydroxide and one part hydrated lime together, you raise the concentrations of potassium, calcium and magnesium together in solution. ”

    How so?… there’s no magnesium in either compound

    Reply
    • Rubert,
      Here in the US, most of our hydrated lime is either magnesian or dolomitic hydrated lime which is typically has a ratio of 5:3 calcium hydroxides to magnesium hydroxides. High calcium hydrated lime has is more like 10:1 calcium to magnesium. That’s a good thought to bring up though, and one reason why we tell folks to read their label to make sure that their hydrated lime contains magnesium in decent quantities. For the most part though, here in the states almost all of our hydrated lime is derived from dolomitic limestone of some sort, so we’re typically pretty safe in assuming that we’ll be supplementing Mg. . .

      Reply
      • Ah, OK.. here in Australia hydrated lime is usually 90-95% pure, and only contains 1% magnesium.. with other impurities like Silcon OXide, Iron Oxide, Aluminium Oxide etc..

        Reply
  3. Thanks for your informative videos/blogs. You mentioned Hydrated lime (calcium hydroxide) is made by combining magnesium hydroxide and calcium hydroxide. My DWC raft system has always had a sodium accumulation rate which was higher than I should be seeing with RO water inputs and no direct sodium use anywhere and I basically put it down to the salt fraction in the commercial feed I use. However, your description of the preparation of hydrated lime has prompted me to check and now made me aware that the varying commercial CaOH manufacturing processes can also include mixing sodium hydroxide and calcium chloride solutions. Without any detailed components description on the CaOH product I’m using, it leads me to believe this might be the case with my sodium accumulations. I do supplement with Epsom salts quite often.

    Reply
  4. “The easiest way to do this is to add all three together. One way to do this is to use hydrated lime and potassium hydroxide together to raise pH.

    When you add 1 part potassium hydroxide and one part hydrated lime together, you raise the concentrations of potassium, calcium and magnesium together in solution.”

    How so?

    There is no Magnesium in either Calcium Hydroxide (hydrated lime), or Potassium Hydroxide

    Reply
  5. Hi!
    Isn’t the point of aquaponics that the nutrients come from the fish waste? It seems that you supplement a lot of nutrients making it into a aquaponic/hydroponic system. Why not use a more nutrient rich fish food instead of adding minerals?

    Reply
    • Hi Niklas,
      Unfortunately, many fish feeds don’t contain enough of certain nutrients, or the forms they contain are unavailable. This means that almost all systems will need supplementation of some sort- especially in systems with crops that take up a lot of nutrients. Using fish food that is more nutrient dense can be a solution sometimes, but isn’t always cost effective or even possible to buy.

      Reply

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