Testing iron levels - The Planted Tank Forum
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post #1 of 4 (permalink) Old 02-17-2019, 03:07 AM Thread Starter
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Testing iron levels

I've been dosing with API Leaf Zone, which gives its composition as 3% K2O equivalent and 0.1% iron equivalent as chelated iron. I don't have obvious signs of chlorosis in the tank, but some young leaves are a trifle light, so I got a Seachem iron test claiming to measure iron to less than 0.05 mg/l. The test showed no iron detectable in my aquarium water.

I calculated the dose needed to give the entire tank 0.25 mg/l and applied the dose this morning, then tested my water an hour later, after there had been time for thorough mixing. No iron detectable.


I then mixed some of the Leaf Zone with distilled water, at what should have given a value of 1 mg/l. Check my math: 0.1% iron in the Leaf Zone is one part per thousand, which means one ml Leaf Zone per liter in my test solution should yield one mg/l. That's what I mixed up (actually, half an ml in a half liter.) I was out all afternoon and did not do my final check on the test for several hours, so there was plenty of time for the test to register. Still no iron detectable.

I used the calibration solution provided with the test, and it registered as expected. This is not chelated iron, but raw reduced iron; but the test kit claims that chelated iron can be measured, if you simply give the test a full hour or more to register.

My conclusion from this run of experiments is that the test is not, in fact, capable of measuring EDTA-chelated iron (I checked the API web site to confirm that this is the chelating agent used.)

Anyone see other possibilities, or any other hole in my logic?
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post #2 of 4 (permalink) Old 02-17-2019, 03:30 AM
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I've not used API Leaf Zone but used both EDTA-chelated iron and DTPA- chelated iron and used a Hanna checker that has detected with no issues the Fe levels very close to the amount dosed.
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post #3 of 4 (permalink) Old 02-17-2019, 04:34 AM
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I cannot say anything about the iron in your fertilizer. However you should be aware that plants need 14 elements to grow. Leaf zone one has 2 of them. It is a very poor fertilizer for aquariums. I wouldn't worry about your low iron readings from leaf zone. Instead I would suggest you switch to using Nilocg.com Thrive or Aquarium coop Easy Green fertilizer.

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post #4 of 4 (permalink) Old 02-17-2019, 02:31 PM
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Seachem Fe instructions say “For chelated iron, allow colour to develop for 30 to 45 minutes or until the colour no longer darken.”

Because it doesn’t work, I emailed Seachem with documented details. They replied with automated BS email about me not understanding how fast plants “utilize” iron. So I replied that plants are not involved and the test is done with demineralized water. Seachem did not reply since. How typical.

Anyway, I found a solution.
DTPA Fe takes 48 hours to detect and reads 1/2 of the actual concentration.
EDTA Fe takes 24 hours to detect and reads 1/2 of the actual concentration.
Unchelated Fe is detected correctly in minutes.

The test plate is so tiny it needs demineralized water additions to compensate for evaporation and stirring. And for aquarium use, any detectable level should indicate enough.

A 1 ppm Fe DTPA 24 hours
B 1 ppm Fe EDTA 24 hours
C 0.4 ppm Fe Seachem sample 1 hour

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Last edited by Edward; 02-18-2019 at 09:18 PM. Reason: Added link
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