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Knowing When to Add Iron to Your Aquaponic System

Knowing When to Add Iron to Your Aquaponic System

This low iron condition has several adverse effects on the plant and is much more serious a condition then just looking pale and yellow.  Low iron levels compromises the plants ability to make chlorophyll. It also is essential for the plant to synthesize proteins and absorb necessary nutrients such as nitrogen and phosphorous. For the backyard gardener, waiting for this indication is certainly tolerable however for the aquaponic farmer whose livelihood depends on healthy, desirable crops, how can we insure that a Basil crop is at the utmost quality and color every week or every day when it goes out to multiple customers? Waiting for that deficiency to show its color, or lack of, for a crop such as Basil that has to go into a Chef’s vibrant green Pesto is too late. So what can we do?

Non deficient leaf on left, iron deficient leaf on right

(image credit – Texas AgriLife Extension)

One option is to routinely add iron to the system. This can surely insure that there is an adequate amount of iron, but if that iron is not being absorbed as frequently as it is added, how would we then know if it is too much? There are indicators for excess iron as well and it can actually cause greater problems then having an inadequate amount. Whereas plants need iron to create Chlorophyll, too much can cause the chlorophyll to change and then inhibits the plant’s ability to absorb sunlight and the energy it derives from it. Too much iron can also impede the plants ability to take up nutrients and absorb sugars and once these vital processes are impaired the plant begins to fail from within and eventually will die. Really then we can actually be creating a greater problem by oversaturating our systems with iron. The other effect is that Chelated iron at a 13% strength, which is what we use, is not cheap. Depending upon where it is purchased it can be as much as $16 or more per pound so having a way to manage how much iron to add can be crucial.

If waiting for the deficiency to appear or risking adding too much iron are neither a desirable alternative, then we need a way to identify an adequate presence of iron in our systems and the solution to that is an iron test kit. This can be found usually at a jacuzzi supply store. Here this simple test can indicate iron levels in your water in parts per million or ppm. After much testing and monitoring we have finally identified where the low range is for our system and how much iron to add to get to what is our desired range. A reading of 1.5ppm is just a touch too low and when getting a reading of 1.5ppm, the plants are just beginning to show a deficiency. Therefore with our weekly monitoring we are looking for a reading of 2.0ppm and then we add either 2 or 4 cups of a powdered, 13% chelated iron. Each 2 cup addition is first mixed in a bucket of water to dissolve the powder is then added at various places throughout the system and each 2 cup addition will move the iron measurement 0.5ppm. In addition to raising the iron level, adding the chelate also causes a noticeable yellow or amber hue to the water and there is a quick “greening up” in the plants sometimes noticeable within 12 hours or a day.

Since implementing this process at our farm, we no longer see iron deficiencies in our plants and have minimized the risks of adding an unmeasured amount of iron that might create an excess and also avoid incurring an additional expense from adding too much. Some advocate using things such as a rusted piece of metal as a source and this may be suitable for backyard or hobby systems but we recommend using a chelated product and implementing a similar procedure so iron additions are a metered and measured addition to your system much like additives to alter pH, especially if you are growing for profit. As farmers, controlling as many variables as possible can help insure a good quality crop, satisfied customers and help protect your bottom line.

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Comment by Widodo Sukardi on February 8, 2014 at 7:19am

A very useful info...

Comment by Sylvia Bernstein on August 11, 2013 at 1:35pm

I was just reading through this and wanted to let you all know that we are now carrying an iron testing device called an Iron Checker by Hanna Intruments -  This inexpensive little device will quickly give you a digital read on your iron levels before you start seeing yellow. ;-)

Comment by Gina Cavaliero on May 13, 2013 at 2:24pm

Thanks Chris and James. 

Chris, I'm still looking for a more reliable test kit too but at least the variance for iron is not near as critical as testing for something like pH especially when we are really just looking for a bottom limit to indicate when to add, which I bet we have to do much more frequently then you.  That's the difference between living on a sand bar and on a big rock! ;-)  

Glad my post helped James!  

Comment by James Stratton on May 11, 2013 at 5:44am

A most excellent post! I have a hobby system, and thanks to your skill in making this information pertinent to everyone, I can avoid any future iron deficiency in my system. You also so correctly pointed out the quick results of adding iron (chelate) to the system. The photos you choose showed exactly what my plants looked like but having not read this blog post yet, I struggle at my diagnosis and added iron only as a guess. Thanks again for a wonderfully informative post!

Comment by Chris Smith on May 11, 2013 at 12:54am

Great info Gina! I never was able to find a reliable iron test kit. I have become used to my systems requirements and dose regular every month. Some varieties of plants will show an iron deficiency earlier than others and I have come to rely on them as indicators.


Comment by Gina Cavaliero on May 7, 2013 at 7:18am

Hi Vlad, thanks and thank you for the interesting reply.  What you describe is certainly something I'd like to learn more about but you probably hit the nail on the head(and not a rusty one! ;-) in that it is likely something that wouldn't be feasible in a commercial setting. Maybe I'll have to just satisfy my middle class boredom with it one day. 

Comment by Vlad Jovanovic on May 5, 2013 at 2:41am

Good stuff Gina Thanks.

Throwing some rusty nails into a grow bed or fish tank is most certainly pretty useless for plants, and not advisable...That said, it is entirely possible to create plant usable Fe2+ (also called ferrous iron and according to the new IUPAC standards is now written as Iron(II), from largely plant un-usable Fe3+ (Fe3+ is the domain of rusty nails...also called ferric iron and now written as Iron(III)

We set up an environment for bacteria to process a largely unusable form of nitrogen (N) in the form of ammonia (NH4/3) to a more plant available form (NO3)...something similar can be done for the conversion of Fe3+ to Fe2+. You then need to chelate the the Fe2+ yourself to keep it from re-doxing back to an unusable Fe3+ form in the presence of oxygenated water. People have been doing just that for about a thousand years or so in these parts, so it's not exactly 'new' or rocket science. But it does take a bit of time, knowledge, will and a special type of insanity/curiosity to want to 'bother' with it...

It's different bacteria in a different kind of environment, and done correctly, can be totally 'meterable' and 'productive' 

I guess as with anything, there is a right way and a wrong way to do it (like when folks set up a super stocked fish tank with only an NFT bio-filter, no mechanical filtration, and then six months later bitch about how AP sucks and doesn't work really work at all). Anywho's...

Making and chelating your own iron probably has no place in a busy commercial setting, and is probably better suited for STEM projects, back yard doomsday preppers, folks who are into self reliance, or live in ridiculously isolated regions, retirees on a budget with time on their hands, even bored middle class white folks for whom the novelty of ammonia/nitrate conversion has worn off, and would like to take the AP adventure/learning experience further...

Comment by Gina Cavaliero on May 4, 2013 at 9:45am

Thanks and your welcome Sylvia!  It was something we needed to figure out not only for our own crops and system quality but I recall a year or so ago, a hydro guy blasting me for stating that we and aquaponics in general used the plants as an indicator of low iron.  His point was that its already too late then and I agreed!  

I've been determined since to have a means to test and to also do the research to see what the low end of the range was so that the iron level could be maintained.  Once I started doing that and learned that too much iron could be even a greater problem, it was even more critical to find a way to monitor, measure and meter especially as iron demands change in a system depending upon the crops.  Also low iron levels could easily have an effect on our crop quality and we needed an accurate process instead of a guessing game.

The test kit we use is by Hanna Instruments however we would be thrilled to find a digital meter.  For a commercial setting, we've grown to love our pH and temp meter as an incredible way to have a constant pulse on the system and we now fine tune our pH like crazy and it has made a significant difference in system performance.  I have to admit I totally geeked out on our meter and with the use of of some IT tools now have constant readings I can analyze and see how they relate to other parameters.  Its very cool. :)

I agree on the "rusty nail" theory, but I've seen it recommended often so aside from it being unmeterable, its  probably largely unproductive too.

Comment by Sylvia Bernstein on May 4, 2013 at 9:01am

Fantastic information, Gina!  Thank you.  What is the brand of Iron test kit that you are using? BTW, my understanding of the form of iron from a rusty nail - iron oxide - is much less available to the plants than iron chelate so that is why it is just a bad idea overall to use rusty nails.  

Comment by Gina Cavaliero on May 4, 2013 at 3:32am

Sure Chris and thanks.  Our system is just over 20k gallons.  

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