# [Wet Thumb Forum]-Newbie Q about iron deficiency



## warhau (Jun 9, 2003)

I am wondering if plants who are iron deficient will catch up and slow their consumption rate once the deficiency is satisfied.

I ask because I have been dosing about 30ml per day of Flourish Iron for ~110g water for about 5 days. This will take the level (according to Seachem Fe test kit) to between .1-.2ppm. 24 hrs later, Fe levels are untraceable again.

Just wondering if this is a permanent regiment, or if it will slow down eventually. Nitrate and phosphate levels are fine with regular 30ml normal Flourish dosing 2-3x per week.

Tank appears in good health. Showing minimal brown algae during 3.5 week cycling on nana.

Full tank specs and photo journal


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## warhau (Jun 9, 2003)

I am wondering if plants who are iron deficient will catch up and slow their consumption rate once the deficiency is satisfied.

I ask because I have been dosing about 30ml per day of Flourish Iron for ~110g water for about 5 days. This will take the level (according to Seachem Fe test kit) to between .1-.2ppm. 24 hrs later, Fe levels are untraceable again.

Just wondering if this is a permanent regiment, or if it will slow down eventually. Nitrate and phosphate levels are fine with regular 30ml normal Flourish dosing 2-3x per week.

Tank appears in good health. Showing minimal brown algae during 3.5 week cycling on nana.

Full tank specs and photo journal


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## Rex Grigg (Jan 22, 2004)

Don't waste your time testing for iron. Dose the tank to get it to 0.1 ppm and then watch your plants. Iron test kits are not very accurate to start with and iron does strange things in the tank.

You say you are dosing Flourish and your NO3 and PO4 levels are fine. Flourish doesn't contain any NO3 and PO4. Did you mean to say you were dosing the Seachem Nitrate and Phosphate products? If so we need to talk.

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## warhau (Jun 9, 2003)

Sorry, that was a non-sequetor. I am dosing Flourite regular also. I just mentioned the PO4 and NO3 levels to show that other main stuff is not being depleted, just iron. I started testing iron and dosing it regularly in the first place because some nana leaves have green veins and yellowing leaves. The plants seem a lot greener with the extra iron, but I will slack off it if you think it is not needed.


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## Roger Miller (Jun 19, 2004)

warhau,

It don't think it's the iron that isn't needed. It's the iron testing that isn't needed. 

If you want, you can adjust your iron dose by decreasing it until you see yellowing again, then dose at a level that is just high enough to prevent the yellowing. That whole process should take a couple months.

Roger Miller


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## warhau (Jun 9, 2003)

Thanks Roger,

Still being a newbie, maybe you could help explain a little better what the problem is with iron testing and iron dosing. 

I am confused, because Jared's Planted Tank Resource fert section mentions Fe as one of the "helpful" things to test for, and Tom Barr's article mentions Fe levels of .2-.7ppm being important for plant growth. 

The Seachem test could be slightly inaccurate, but the difference between clear/yellow (untraceable) iron and purple tinge (some iron) seems like it would be fairly foolproof.

Maybe you could point me to some articles, posts, or more info on inaccuracies of Fe testing, and problems with iron dosing. I trust you. I would just like to understand better.

Thanks


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## Roger Miller (Jun 19, 2004)

> quote:
> 
> Originally posted by warhau:
> Still being a newbie, maybe you could help explain a little better what the problem is with iron testing and iron dosing.


Now there's an involved subject. I'll see what I can do.

First, iron is a trace nutrient; plants only need very small amounts of available iron -- something close to 0.056 parts per *billion*, according to one source.

Second -- and this is the bugger -- iron doesn't stay dissolved in water under normal conditions. It forms insoluble mineral preciptates and a variety of complexes. Many of the complexes that iron forms are so strong that they make the iron useless to plants.

Third -- and here is the man-made complication -- fertilizers that contain iron normally contain it bound up in a kind of complex formed between iron and an organic molecule. The complex is called a chelate. The word "chelate" comes from the Greek (I think) word for claw and "claw" describes the shape of the complex. The organic molecule wraps around the iron atom like the talons of a falcon's claw wrapped around a mouse. The complex isolates the iron atom from many reactions.

There are several different kinds of iron chelates that are used in fertilizers and each has distinctly different characteristics. Iron EDTA is used in many fertilizers. I think that Tropica uses iron DTPA. Seachem uses iron gluconate. Iron citrate is another option. There are many others. The various iron chelates can be divided into two groups, weak chelates that plants can break down to get to the iron and strong chelates that plants cannot break down. Iron gluconate and citrate are fairly weak chelates and are in the first group. Iron EDTA and DTPA are very strong chelates and they belong in the second group.

The weak chelates like gluconate and citrate don't stay in solution very long. Plants remove the iron and/or the chelate breaks down. Those additives need to be used frequently and in small doses.

The strong chelates like EDTA and DTPA stay in solution longer. The chelates are eventually broken down by light and slowly release very low concentrations of iron into solution. After it is released the iron remains only briefly in a form that plants can use before it either forms an insoluble mineral or is once more combined into a strong complex. The strong chelates are added in higher doses than the weak chelates and they should be used less frequently.

Iron testing -- even assuming that you have a perfect test kit -- is a complicated process because of the different chelates that are used and the ability of the test reagents to detect different forms of iron. Most of the commercially available kits are not made to test iron bound in strong chelates. We rarely know if the test is actually telling us about all the iron, or just parts of it.

Another problem with hobby level test kits is that when they work they detect iron only at levels that are much higher than the levels that are meaningful to plants. It isn't of much use to know that your water has 0.X ppm of iron in some unknown and probably unavailable complex, when the only thing that really matters is that the water should provide a very tiny amount (say 0.000056 ppm) of iron in a very specific form.

Perhaps even more important, the test kit only tells you what's in the water. Rooted plants have access to potentially large reserves of iron in the substrate. That iron does not appear in any test.

The last problem with iron tests is that a lot of the kits that are available in the hobby are not very good.

What it comes down to is that the test result does you about as much good as a wild guess. The test don't do nearly as much good as watching your plants carefully and experimenting with dosing levels over time.



> quote:
> 
> I am confused, because Jared's Planted Tank Resource fert section mentions Fe as one of the "helpful" things to test for, and Tom Barr's article mentions Fe levels of .2-.7ppm being important for plant growth.


Most hobbyist experience with iron testing came from using PMDD. In that method, an iron test was often used to regulate the dose of trace elements. The trace element mixes used in the hobby and most of the common iron fertilizers use iron EDTA. The concentration levels that are cited in most sources are *maybe* useful if you use iron EDTA. Otherwise they are not useful. Right or wrong, Tom's advice to use 0.2 to 0.7 ppm is higher than anyone else's. I'm not sure why, but I believe it is based on his experience.

If you can get a test kit that reliably tests for iron EDTA levels and if your lighting is about the average in both level and spectrum for the people who reported their experience then it may be reasonable to keep something like 0.1 ppm of iron EDTA in the water. I have done some calculations and found that for common aquarium conditions those levels may be needed to get the right amount of plant-available iron in solution. For conditions in your tank and for other chelates you would need other levels. We don't have enough experience in the hobby to provide correct levels for all chelates or for all types of tests under all conditions.

The practice of using an iron test to regulate trace element doses is something that I think should be avoided. The chemistry of chelated iron is very different from the chemistry of other trace elements and their compounds. If an aquarist depends on an iron test to regulate dosing then they could easily build up levels of some trace elements (copper, for instance) that are damaging to plants and lethal to some animals.

Incidentally, I asked Greg Morin of Seachem how they arrived at a recommended dosing level of 0.1 ppm. He told me that they didn't do any testing to establish that level. They cited the 0.1 ppm target concentration on their label only because that was the popular number often quoted on APD. People who try to use Flourish iron to maintain that level invariably end up using a lot of fertilizer. That is unnecessary for the plants, but good for Seachem.



> quote:
> 
> Maybe you could point me to some articles, posts, or more info on inaccuracies of Fe testing, and problems with iron dosing.


The APD archives are always useful. Otherwise you need to get pretty technical to use much published information.

As is true for almost any topic in planted aquaria, the best single source of technical information is Diana Walstad's "Ecology of the Planted Aquarium."

The best summary article I've ever read about iron in plants is "Absorbcion y Asimilacion de Hierro in Las Plantas" by Adalberto Benavidez Mendoza. I thought enough of that article to interpet it (lamely) to English. It is available online at Steve Pushak's web site:

http://home.infinet.net/teban/iron/ironw.html

Have fun,
Roger Miller


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## warhau (Jun 9, 2003)

Wow! Thanks Roger! That is just what I needed. Hopefully you can archive that response so the next time someone asks what the deal is with iron, you can save yourself some carpal tunnel syndrome. Thank you very much for the very informative and thorough reply.


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