# A lot of discussion about Fe; what about Manganese (Mn)?



## nfrank (Jan 29, 2005)

Given the recent discussions about supplemental Fe dosing, stability and availablity of various forms of water soluble iron, i got to think about the amounts of Fe vs the other traces. Reading APC and other aquarium plant forums, there is strong user evidence that additions of Fe on top of a basic mix of trace elements can improve plant health, increase color, shine, and generally produce positive results. If everything else is in balance, then this also wont cause algae.

We know that unless soil is used, the water column should get a good mix of all the trace elements. I was wondering how important are the relative amounts. Fe and Mn are the two most prevalant trace elements, but seem to be provided in many different ratios.

Here a table of 4 common sources of these nutrients and their included percentages. Clearly, the Fe:Mn ratios are quite varied.

*...........................Fe ......... Mn...........(Ratio)*
Miller Microplex.....	4%......... 4%......... ..(1.0 )
Plantex CSM..........6.53%.....1.87%........(3.5)
Tropica TPN..........	0.07%.....0.04%........(1.8)
Seachem FL.........	0.39%.....0.01%........(31.1)

When additional iron is added (as FL iron, Fe-DTPA, or Fe-EDDTA), those ratios can further increase. In fact, combinations with Fe-DTPA or Fe-EDDTA can produce ratios that match some of the others (e.g. 1 part Miller plus 2 parts 10%FeDTPA yields a 2:1 ratio which approximately matches TPN)

I could not find very many references to desirable ratios. Occasionally, the ratio of 2:1 is mentioned, which conforms to the amounts in Tropica's liquid. For many years, i have treated that as the "gold standard."

One reference that supports this particular ratio is Adriano DC: Manganese. In Trace elements in terrestrial environments. Biogeochemistry, bioavailability, and risks of metals. 2nd edition. New York, Berlin and Heidelberg: Springer; 2001:547-585. Adriano [9] described a biochemical antagonism between iron and manganese and indicates that "the Fe/Mn ratio should be in the range 1.5 - 2.5"​
However, other references just say the ratio should be greater than one. Plant Analysis

If we test for trace elements, we probably only test for Fe; and use that test as an indicator of the other traces. The validity of simple colorometric tests, however, and what species of iron they detect is beyond the scope of this post. Observing plant health and appearance may be a much better tool. One complication is the similarity between Fe and Mn deficiency. For Mn, it is dead yellowish tissue between leaf nerves. For Fe, leaves turn yellow and greenish nerves enclosing yellow leaf tissue. Another factor is stability of chelated Fe and Mn. Supposedly, Mn-EDTA is reasonably stable. However, it has also been said that excess Fe can induce the Mn deficiency! So, how much Fe and of what form will be too much?

Some of the above seems to contain some contradictory information. Is it plant specific, concentration related, connected to pH, the suite of other nutrients including hardness minerals, or what. It is hard to argue with growers positive experiences, but i wonder if there are conditions when Fe to Mn ratios become more important. Or do we just ensure there is sufficient Mn, and not worry about increasing the ratio?


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## wet (Nov 24, 2008)

Hi Neil,

I've not played with Mn nor think I can make hobby time for it any time soon, but I added Mn and Cu calculations for Plantex and MicroPlex to this calculator in hopes it helps you and other people conduct this experiment. I hope it helps.

http://wet.biggiantnerds.com/fe_calc.pl


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## Bert H (Mar 2, 2004)

You bring up some good questions. My gut feeling would be to say that one should have sufficient Mn available (as long as you are not in the toxic range), and not be overly concerned about ratios. 

There are ways to test these questions. Unfortunately, I don't know of many of us who would be willing, or able, to set up multiple identical tanks and vary only one variable at a time to see cause/effect thereof. Then the question would arise whether one specie would have the same exact needs as another? 

I think most folks when first starting out want to have the exact ppm of nutrients known, measured, etc. As time passes and we become more experienced in the hobby, we realize exact, absolute numbers are not as important as visual clues and how to interpret them. Chefs add a 'pinch of this and a pinch of that', folks who aren't as versed need to know to add a 1/4t of this and a half tsp of that. 

Hope that made sense.


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## Diana K (Dec 20, 2007)

From a chart in Diana Walstad's book, page 105:
The critical concentration of Mn and Fe in _Elodea canadensis_ are: 
Fe: 60 mg/kg
Mn: 4 mg/kg

In a laboratory analysis of her plants (I think it was assorted aquatics, not specifically Elodea):
Fe 200 mg/kg
Mn: 350 mg/kg

So there seems to be quite a range there of what will work to keep the plants alive. 
As for dosing either or both... I dunno. Are either of these available in the substrate, or from fish food in forms that plants can use and at levels that are useful?
I use CSM+B and chelated Iron and do not notice a deficiency that would point to either Fe or Mn.


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