Join Date: Feb 2019
Location: Los Alamos, New Mexico
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?