Nutrient Supplementation in Commercial Organic Aquaponics (Part 2)

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Part 2What is the best way to introduce the products discussed in Part 1 for supplementation into my commercial organic aquaponics system?

Written by: Michael J Brooks, Technical Supervisor – Green River Greenhouse; Peru, Indiana



In last month’s ‘The Scuttlebutt’ I discussed some of the preferred products for nutrient supplementation of your commercial organic AP system.  In Review: I covered the more common nutrient deficiencies in an aquaponics operation; iron, calcium, and potassium. I then went over the options available to a certified organic farm for supplementing those deficiencies.  The three that I recommend; Lingosulponate for iron (available here), calcium carbonate for calcium, and potassium sulfate for potassium were explored thoroughly, as well as compared to any other products determined to have met the criteria for organic farming.  In this, the final installment of a 2 part discussion I will take a look at the process of getting those products into your system water, measuring their presence in your system water, and determining how often the supplementation process should be repeated for each.

Before adding any nutrients to your water you should first look at what is currently available in the water, and at what level.  Compare these findings to what is considered the optimal range to determine how far you need to climb.  Keep in mind I am referring to the three nutrients that are extremely likely to be lacking in your AP system, and thus the eventual supplementation of each is inevitable.  How much supplementation will be the unknown variable you will want to determine before you begin the actual process.

Listed below are the acceptable ranges for the three nutrients I mentioned, as well as some other important levels that one should try to achieve in their system.

Optimal Ranges for Important Micronutrients in Aquaponics:

  • Iron            Between 1 and 2 ppm
  • Calcium Between 40 and 70 ppm
  • Potassium  Between 40 and 70 ppm
  • Magnesium Between 40 and 70 ppm

Acceptable Ranges for other Important Water Tests in Aquaponics:

  • Carbon Dioxide 0 to 30 ppm
  • Chloride     0 to 5000 ppm
  • Oxygen 3 to 10 ppm
  • Nitrite 0 to .8 ppm
  • pH 3 to 7.5 ppm
  • Hardness 5 to 350 ppm
  • Alkalinity 50 to 250 ppm
  • Ammonia 0 to .4 ppm

IRON. Supplement using lingosulphonate.  This product does not need to be cut with water and can be added directly to your systems grow beds and/or raceways.  Start with small amounts depending on your system’s overall size (it is never a bad idea to start with less product).  Whatever amount you decide to start with, make sure you are keeping a close eye on the levels as you dose your system.  When you start to notice a spike in your daily readings you should stop adding the iron to your system.  Continue to take daily readings and record the rate at which the levels decrease.  (How fast is your system using the iron you are introducing?)  Remember: you should work to achieve the optimal reading(s): depicted in the list above.  Eventually you will begin to understand how the iron is being used by your particular system, and what you need to do, in regards to supplementation, to maintain that recommended reading.

CALCIUM. Supplement using calcium carbonate.  A powdered product, calcium carbonate can be slightly tricky to introduce to your system.  Again, you should start with a low amount, 50 to 100 grams, depending on your system’s overall size, and it is never a bad idea to start with less.  The powder needs to be dissolved in water and dripped slowly into your system.  This is where the tricky part lies, as you will find the powder is difficult to dissolve at times.  Some ways to help you with this are: use warm RO water to help breakdown the product, use an aquarium-size air-stone to keep the warm water and the product in suspension, and you can also use some sort of paddle wheel on a cordless drill to mix the solution as well.  Another thing that some people do with calcium carbonate is the use of a mesh bag: put the product in the mesh bag, the mesh bag inside your drip/dosing tank, and simply squeeze around on the bag to help the product break down.  The mesh will ensure that clumps and such are not getting through the plumbing of your dosing tank and the calcium is not getting added to your system in large sudden quantities.  It is important to manage a slow addition of the product or you could seriously risk tanking your system’s pH.  Another thing with calcium is that you must pay close attention to how it is being taken up.  You can observe this easiest by simply noting the rate at which your readings decrease.  The uptake of calcium is passive, meaning it will occur as your crops draw in water.  An environment rich in humidity may cause plants to fail to transpire (let out water) properly.  In turn, the calcium uptake will decrease, as well as the uptake of nutrients in general.  If you feel like you are dosing your system heavily yet you are seeing little to no change in your readings, you should check the conditions of your environment.  If your readings are depleting extremely quick you should consider slightly larger doses.  In spite of a required level of 40 to 70 ppm, it is a good rule to just keep it under 100 ppm.  When you approach levels of 120 ppm you have entered the danger zone and will start to effect the uptake of other nutrients.  You should immediately back off of your dosing amount.

POTASSIUM. Supplement using potassium sulfate.  Unfortunately this is currently the only product available to organic AP growers for the supplementation for potassium.  In many cases this alone has caused many AP farmers to forgo the idea of certified organic in the first place.  The product will often cause the fluctuation of your systems pH in large swings.  It can be done despite these issues however, but not without the close observation of you the grower.  Good record-keeping, and the understanding of those records are not only key in making the potassium supplementation using potassium sulfate work, but all in making your entire operation successful on any level.

The application of potassium sulfate should be done in precisely the same method as the calcium carbonate.  One fortunate aspect of this product is however, that you will have very little trouble getting it to dissolve.  No mesh bags or paddle wheels needed.  I always recommend the use of warm RO water though, as it will always speed the process up.

In addition to the way they are added to your system, calcium and potassium are closely related otherwise.  For this reason, if you were to add too much calcium to your system you could lock out your crops to the potassium.  The best way to avoid this is by working hard to achieve a balance of not only these two nutrients, but of magnesium as well.  You can get around some of these issues by electing to use foliar sprays instead.  However, foliar sprays come with their own list of concerns; perhaps we will discuss foliar sprays in a future column, and at that time you can make your own decision.  Although, for what it is worth, and as far as organic production goes, I highly recommend the use of the three amendments I’ve discussed.

Remember to always check your pH and monitor any changes in it.  Large swings in your system’s pH is a strong indication of issues with your supplementation of calcium and/or potassium.  In the event you experience like issues you should make calculated changes to your dosing while continuing to monitor the pH situation.  If you don’t feel confident it is always a good idea to consult an authority in the field for recommendations.

Thanks for reading.  Fort now, that’s The Scuttlebutt!

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