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Dupla Fe, K Test

I recently submitted the Duplaplant and Duplaplant 24 fertilizers
from the Dupla fertilizer system for testing to the University of Maine
at Orono's analytical lab which is maintained by their department of
Plant, Soil, and Environmental Sciences.

The results were as follows:
Fe: 13.2 mg/L
K: 140.0 mg/L

Fe: 0.455 mg/L
K: 0.042 mg/L

Testing details
All tests with exception of the Duplaplant24 were performed
using a Plasma AtomComp inductively coupled plasma emission
spectrometer. K testing for Duplaplant24 was performed using a
Thermo Jarrell Ash atomic absorption spectrometer due to its low

Sampling details
2 tablets from two separate lots were diluted in 1L of distilled
water; the solution was than diluted with 1L more of distilled
water to obtain a 1 tablet concentration equivalent.

10 "typical" sized drops were diluted in 1L of distilled water; the
solution was submitted as is for testing and the numbers presented
here adjusted by a factor of 10 to obtain a 1 drop concentration

The recommended rate of dosing into aquaria is 1 Duplaplant tablet per
20L of water change water and 1 Duplaplant24 drop daily per 50L of total
tank water. At those rates, the products would produce iron concentrations
in the tank of 0.66mg/L for Duplaplant tablets and 0.0091 for Duplaplant24
drops. The Duplaplant value seems high and inconsistent with Lamotte test

I note that an earlier post in the Krib also performed Fe and K
testing on Duplaplant tablets. While the sampling than was done
using an unreported amount of distilled water, the proportion of
iron to potassium then (Fe=234 mg/L, K=2480 mg/L ) and now
is highly consistent. This leads to speculation on the value of
the remaining parameters measured in the earlier test to obtain values
when diluted in 1L of water.

Finally, before submission, the Duplaplant24 sample was also
tested for iron using Lamotte test kit model P-62. ( 0.2 accuracy in the
range of 0.05 - 1.0 ) The results were 0.11 mg/L or a deviation
from the spectrometer's results by a factor of more than two (2).
Is this is acceptable at the very low concentrations involved?

Christopher Coleman
christopher.coleman at worldnet_att.net