The Planted Tank Forum - View Single Post - Where is all the iron going? Keep adding more?
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post #4 of (permalink) Old 03-31-2015, 05:15 PM Thread Starter
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I've been trying to read about the behavior of iron in water. A good discussion is here, though the concluding paragraph reads as follows:

Elusive iron. In brief, when an aquarist adds iron to a planted tank, then tests the following day and finds iron levels that are once again untraceably low, there are many routes the iron may have followed, aside from being taken up by the plants or algae: it may have been scavenged by iron bacteria, or abiotically oxidized by dissolved oxygen, it may have precipitated out or co-precipitated, or it may have got bound to an organic chelating compound dissolved in the water, such as one of the extremely various humic substances, tannins or humic or fulvic acids and the like. In more alkaline waters than mine, these humins would be chelating calcium and magnesium in competition with iron, which remains more vulnerable to oxidation. So plants in alkaline water can suffer Fe deficiency, even when the element is plentiful in the system—a less troublesome problem for plants in waters with pH values below 7.0. Iron toxicity in over-fertilized planted aquaria is an unexplored issue, I feel. I would generally prefer to add humic substances, in order to chelate the iron that is already there, rather than add iron to my aquarium systems.
After reading the whole article I understand more of the possibilities but I do not quite know what to do about it. Some paths seem to leave iron available, some do not, and the vague comment about iron toxicity is a bit of a concern.

My main question, I think is simple -- if I use the Seachem test, and it shows negligable iron after 24 hours -- is there any danger of upping the dose until I start seeing some significant amount at 24 hours, say 0.1ppm. Is there any way to build up toxic levels (or other harm beyond cost) of trusting the test at the 24 hour point?

Any good water chemists out there?


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