Iron is an essential nutrient for plants but is difficult to manage in aquaponic systems. Plants use chelation to make insoluble iron available by producing organic molecules that bind to iron. Chelated iron can be added to supplement iron and avoid deficiencies. Chelated forms like FeDTPA and FeEDDHA are recommended because they maintain iron solubility over a wide pH range. It is best to regularly supplement systems with 2 mg/L of chelated iron every three weeks to prevent issues.

1. Understanding Iron in
Aquaponics

2. Iron is abundant but tricky to manage.
To supplement the iron that your plants need, you have to
understand how the element functions within that ecology.
Why Study Iron?

3. This post gets technical.
You might want to access your inner science geek later on
in this slideshow!
Warning:

4. One of the most plentiful elements
on the planet, and one of the oldest
used by mankind.
Also crucial to chlorophyll
development and photosynthesis in
your plants.
Read our full blog post on iron here.
Iron
Fe

5. Constituent of heme
complexes (like hemoglobin).
Essential component in the
production of chlorophyll.
IN ANIMALS
IN PLANTS

6. • No chlorophyll
• Retarded plant growth
• Chlorosis
• No cytochrome
• No metabolism
No iron means...
Fe

7. Unfortunately, because it is
highly reactive, iron is typically
unavailable.
It flits between soluble and
insoluble forms compounds with
other minerals and (in aerobic
environments generally) plays
hard to get.
No iron means...
Fe

8. Iron exists in a variety of ionic states, but prefers these two in
particular:
Abundant but very reactive
Fe3+
Fe2+
Transitions between the two readily
Ferric iron Ferrous iron

9. Fe3+
Fe2+
More oxidized
Unavailable
to plants
Less oxidized
Available to
plants

10. The more oxidized form of iron is
unavailable to plants, but aquaponic
systems require mostly aerobic
environments (Aerobic = Oxygen)
The problem

11. As soon as ferrous iron becomes soluble in aerobic
environments it is often oxidized, (becoming ferric iron)
or reacts with other compounds to become biologically
*unavailable.
*especially at high pH values when different
hydroxides are formed
The problem

12. Many practitioners falsely assume that this will supplement
system iron.
It does add to the system iron, but not in a constructive or
meaningful way. All this does is introduce more ferric iron
to the system - a form that was most likely already there in
plentiful supply.
Solution 1: add rusty stuff to
your system

13. Other growers use dedicated anaerobic zones where
ferric iron will be reduced by the oxygen free, anaerobic
environment to produce ferric iron.
Solution 2: intentional
anaerobic zones

14. This can work in low pH systems, but still does not entirely
address the problem of getting the reduced iron ion (Fe++
)
through the oxygenated aerobic zone surrounding the plant
roots (especially in high pH systems).
Solution 2: intentional
anaerobic zones

15. Plants have their
own solution to
this problem.
The good news

16. You see, plants have some amazing chemical means of
hijacking ferric iron ions, tying them up, bundling them into
the soluble, biochemical equivalent of the panel van, and
delivering them, bound and gagged, to the root surface
for plant use.
The good news

17. Plants also use a few other techniques
to make iron available, including:
- Acidifying the root surface by
excreting hydronium ions
- Secreting iron reducing compounds
For aquaponic growers, chelation is
the key process.

18. Chelation is an aquaponic iron-fixing technique.
Chelation is the process of tying insoluble ferric iron ions and
compounds to organic molecules to make them soluble. It
uses special organic molecules called chelatins. These are
organic molecules that are specifically designed to capture,
or “dissolve” metals like iron.
Chelation

19. So where do chelatins come from?
1) Produced by plant roots and leaked into the soil (e.g.
phytosiderophores, which bind ferric iron, pulling it from
various insoluble precipitates and substances. The grasses
(Poaceae), and especially barley are particularly effective at
producing phytosiderophores for capturing iron.
You need chelatins...

20. So where do chelatins come from?
2) Others: Amino acids, organic acids (especially humic acids
like those from peat), and polyphenols. Can be introduced,
but they aren’t always enough to keep iron available to the
plants - especially in systems with a pH of 7 or above.
3) Chelated iron is often necessary even if you already have
the first two.
You need chelatins...

21. Admissible under USDA Organic standards, chelated iron is
an artificially chelated iron ion - essentially, iron attached to
an organic molecule to make it soluble.
By adding chelated iron, iron deficiencies in your plants can
be avoided.
Chelated iron

22. Forms of chelated iron
FeEDTA FeDTPA FeDDHA

23. This is a slightly toxic form that aquaponic practitioners should
not use.
It should not be used because of it’s toxicity, but also
because it typically only effectively chelates iron up to the
pH range of 6.3 or 6.4. Above this range it is not a stable
chelate.
FeEDTA

24. Recommended for most
sytems at pH values
between 6 and 7.5. It is
commonly available at
lawn and garden stores.
FeDTPA
Shop FeDTPA

25. Recommended for systems above pH values up to 9.0 and
the best-all-around form of iron chelate - especially for
starting systems.
Maintains iron solubility in almost all of the water conditions
encountered by startup aquaponic systems.
*Miller brand can turn water red
FeEDDHA

26. 1) Reactionary - any time you
see a deficiency
Two ways to supplement iron

27. 2) Regularly supplement - 2
mg/L every three weeks
Two ways to supplement iron
*Foliar applications can be used for quick response
but aren’t highly recommended

28. At the 2mg/L dosing rate, a 10
pound, $15 bag of chelated
FeDTPA will lat well over a year,
or less than $1 per month.
Cost of chelated iron

29. - “Miller DP” - DTPA (On the shelf or ordered through Ace
hardware)
- “Sequestrene” - DTPA (5 lb bag on Amazon for $57)
- “Miller FerriPlus” - EDDHA (SunshineGardensFl.com; 1 lb for
$20, or 20 lbs for $300)
- “Sequestar Iron 6% Chelate” - EDDHA (RoseCare.com;
5 lbs for $73)
Chelated iron products

30. Click here.
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31. UPSTART UNIVERSITY

32. Read the whole article
We’ve got plenty of other videos and articles to help you out
if you get stuck.
Check out the full iron post here.
If you’re really stuck, feel free to reach out to us.
Happy growing!