Testing for Molybdenum in Aquaponics

This is part of a series on Aquaponic Water Testing.

Another heavy metal, Molybdenum is necessary and safe to add to Aquaponic systems. Hoagland suggests 0.02ppm, a level we can safely accommodate since the PNEC_Aquatic for Mo is 12.7ppm.

Molybdenum deficiency will include symptoms of nitrogen deficiency. An upward cupping of leaves, and mottled spots turning into interveinal chlorosis may be present. Cauliflower can exhibit a whiptail appearance. While rarely seen, molybdenum toxicity is easy to visually diagnose – leaves will turn a very brilliant orange.

Testing for Molybdenum

While I am listing one color comparator test, most methods that provide the resolution we require will require a photometer/colorimeter.

  1. Hanna HI96730 Portable Photometer (0.0-40.0; Resolution 0.1)
    $209@Amazon meter + $75 / 100 = $0.75ea
  2. Hach MO-LR (0.25 – 3 mg/L)
    $121 / 100 = $1.21ea
  3. Hach DR900 + 8169 (0.02 – 3.00 mg/L; Res 0.02)
    $57.95@Hach / 100 = $0.58ea
    HachDR900 + Hardness (Calcium) Reagent Set, LR
  4. Hach Colorimeter II Moly (0.02 – 3.00 mg/l)
  5. YSI Molybdate LR (0-15; MDL 0.2)
    $35.67/50 OR $73.95/250
    YSI 9300/9500 Colorimeter + YSI-Photometer-Starter-Pack

Know of, or use another method of testing for Molybdenum in Aquaponics? Let me know via the comments and I’ll update this post.


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