Testing for Iron in Aquaponics

This is part of a series on Aquaponic Water Testing.


Iron is one of the most common deficiencies in Aquaponics systems. The main symptom of a deficiency is interveinal chlorosis on the newest leaves of the plant. Many other deficiencies cause interveinal chlorosis, so relying on visual identification can be hard, especially for inexperienced growers.

Aquarium test kits, like the Seachem MultiTest Iron, should be avoided if possible. They lack the ability to accurately check for chelated iron. However, they will answer the question “Is there Iron?”

I own and use the Hanna Checker HI721.

If you use Fe-EDDHA, or Fe-HBED in your system, beware test interference. The YSI MR test is the most accurate test I’ve found. It separates out the Iron Reducer and the phenanthroline reagent, allowing for the photometer to be zeroed in between the two steps.

  1. Seachem MultiTest Iron
    $13.09 / 75 = $0.17ea
    Seachem MultiTest Iron
  2. Hanna Checker HI721 (0.00 – 5.00; MDL 0.01; Resolution 0.01)
$49.13@Amazon Meter + 6 tests.
    $6/25 refills=$0.24 ea
    HI 721 Iron Meter
  3. LaMotte Smart3 + 4315-H (0.0-10.0, MDL 0.05)
    $37 / 100 = $0.37ea
  4. Hach DR900 + 8008 (0.02 – 3.0; Resolution = 0.021)
    $21.95@Hach / 100 = $0.22ea
    HachDR900 + Hach8506
  5. YSI 9500 + Iron MR (0 – 5.0; MDL 0.02)
    $46 / 50 = $0.92ea OR $104.40 / 250 = $0.42ea
  6. YSI 9500 + Iron HR (0-10.0; MDL 0.05)
    $23.49 / 50 = $0.47ea OR $46.98 / 250 = $0.19ea

Have I missed an Iron test that would work for Aquaponics? Let me know in the comments and I’ll update this page.

4 thoughts on “Testing for Iron in Aquaponics”

  1. Hi Scott,

    If “the YSI MR test is the most accurate test”, *and* it’s cheaper than the Hanna Checker HI721, why do you use the latter?

    TIA,
    Jim

    1. The hanna test is quicker, and can be run in parallel with other tests, instead of tying up the YSI photometer for 10 minutes. I’m not currently using Fe-EDDHA so the results from the two are very close.

      Also, the YSI medium range test is not cheaper. The hi721 reagents are 24c/test, ysi mr are 92c/test in small quantities and 42c/test in bulk.

      1. Thanks for the info, Scott. I guess my eyes just went straight to the bottom of your list and saw the YSI high range costs. That Hanna instrument is looking better and better…

        Regarding test interference from Fe-EDDHA/Fe-HBED: Is there a way to mitigate that while using the HI721, e.g. waiting a certain number of days between application of Fe and running the test?

        1. Only three ways to mitigate the red iron chelates.
          1) massive water change. Leaving the top-off hose going for 4 or 5 hours does the trick
          2) apply a correction based on a lookup table (which I’m not comfortable publishing. It works for me, but it’s a hack)
          3) add a tiny amount of Hach RoVer to the sample before zeroing the meter. I believe hach sells a 0.05 g scoop that should be the right size.

Leave a Reply

Your email address will not be published. Required fields are marked *