This is part of a series on Aquaponic Water Testing.
Zinc is necessary for plant growth, but only small amount are needed. A deficiency can show itself as interveinal yellowing and pitting on younger leaves, leading to advanced interveinal necrosis. Leaves may also become smaller with shortened internodes.
Hoagland suggests a zinc level of 0.05ppm. That number should be safe in Aquaponic systems, but anything over that would start to cause problems with invertebrates.
Testing for Zinc
Because of the extremely low levels we are measuring, there are no visual methods available to us. Currently, the Hanna HI96731 is a great deal from Amazon if you don’t own a multi parameter colorimeter.
- Hanna HI96731 (0.00 – 3.00; Resolution 0.01)
Meter: $60@Amazon
Reagents: $48@eSeasonGear / 100 = $0.48ea
I have this meter. It’s fairly easy to use, but in order to use the meter you’ll need reagents, and a 20ml graduated mixing cylinder.
- LaMotte Smart3+3667-01-SC (0.00-3.00; MDL 0.05)
Reagents: $112 / 50 = $2.24ea
+ 
- Hach DR900 + 8009 (.01-3.0; Resolution 0.013)
Reagents: $58.95@Hach / 100 = $0.59ea
+ 
- YSI 9500 + Zinc (0-4.0; MDL 0.02)
$46.11 / 50 = $0.92ea OR 120.06 / 250 = $0.48ea
+ 
Zinc Safety
| Species | NOEC Level, ppm |
| Bluegill | 0.226 |
| Rainbow Trout | 0.291 |
| Tilapia | 14.0 |
| Hyalella Azteca | 0.043 |
| Daphnia | 0.021 |
Adjusting Zinc Levels
National Organic Program states: Zinc carbonate, zinc oxide, zinc silicate, and zinc sulfate may be used to correct a documented zinc deficiency., 205.601(j)(6)(ii) As plant or soil amendments… Micronutrients—not to be used as a defoliant, herbicide, or desiccant. Those made from nitrates or chlorides are not allowed. Soil deficiency must be documented by testing.
I use zinc sulfate. I ordered a 1lb bag from Ebay, and was sent a 5 lb bag instead. At my current rate of usage, that should last me several hundred lifetimes.
Know of another way to test for Zinc in Aquaponics? Or have a different supplement regime? Let me know in the comments and I’ll update the page.