# [Wet Thumb Forum]-Substrate iron



## Roger Miller (Jun 19, 2004)

At the AGA conference this weekend I had the very memorable opportunity to talk with Diana Walstad. One of the first questions that came up was "What's with these people who are growing plants in high-iron substrates and still adding iron to the water?"

"Good question." Thought I.

My first reaction was that a lot of people are adding iron without knowing whether or not the plants need the extra iron. They're following directions, following a formula or depending on meaningless test results instead of paying attention to the plants themselves. Even those who do pay attention to the plants may interpret non-diagnostic deficiency symptoms as indicating a lack of iron when the symptom is actually caused by a lack of zinc or some other nutrient.

Later I thought back over my own experience in setting up my 150 with Flourite, which is a high-iron substrate. It seems like there must be other explanations. The evident alternative is that the iron in those high-iron artificial substrates is -- unlike the iron in most soils -- unavailable to plants.

I have my own thoughts on why and I'll probably get around to posting them. Does anyone want to beat me to it?

Roger Miller

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_"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein_


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## Roger Miller (Jun 19, 2004)

At the AGA conference this weekend I had the very memorable opportunity to talk with Diana Walstad. One of the first questions that came up was "What's with these people who are growing plants in high-iron substrates and still adding iron to the water?"

"Good question." Thought I.

My first reaction was that a lot of people are adding iron without knowing whether or not the plants need the extra iron. They're following directions, following a formula or depending on meaningless test results instead of paying attention to the plants themselves. Even those who do pay attention to the plants may interpret non-diagnostic deficiency symptoms as indicating a lack of iron when the symptom is actually caused by a lack of zinc or some other nutrient.

Later I thought back over my own experience in setting up my 150 with Flourite, which is a high-iron substrate. It seems like there must be other explanations. The evident alternative is that the iron in those high-iron artificial substrates is -- unlike the iron in most soils -- unavailable to plants.

I have my own thoughts on why and I'll probably get around to posting them. Does anyone want to beat me to it?

Roger Miller

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_"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein_


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## gpodio (Feb 4, 2004)

Two questions come to mind:

1. Do some plants prefer foliar uptake of iron?

2. At what rate is the iron being made available to plants from the substrate? Perhaps not quickly enough to satisfy the immediate needs of some plants?

Giancarlo Podio


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## anonapersona (Mar 11, 2004)

And why, when I add a bit of liquid iron, does my Sunset Hygro get redder for about 4 days, but when I add a ml or two of Seachem Excel to the same 30 gallon tank, the Sunset Hygro much redder, for almost 2 weeks?!?

This tank has 100% Flourite, but a bit of Excell produces an iron type response better than iron. So, maybe it is the chelation?


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## Roger Miller (Jun 19, 2004)

Here's the long, sad story as I see it.

Plants need rather little iron. Depending on the source you read, terrestrial plants need 1E-6 to about 1E-9 molar of iron in solution -- that is .00006 to 0.06 ppm. At lower concentrations the plants show evidence for iron deficiency. There are variations between plants -- even between strains of plants -- but I have no reason to believe that the needs of the large and varied group of aquatic plants is systematically different.

Three factors help make iron available to plants growing in soils; low pH, low oxidation potential and high surface area.

Iron is almost always present in soils at high concentrations, but it is in or on the mineral grains in the soil, not dissolved in the water. The concentration of iron dissolved in a soil (aquatic or not) is strongly influenced by the solubility of iron hydroxides in or coating the mineral grains. The hydroxides can dissolve through several different paths leading to either ferrous or ferric ion in solution, but the amount of iron in solution depends on the pH of the soil. If the soil pH is over 5 then the concentration of dissolved iron is too low to support normal plant growth. In soils the pH is kept low by CO2 and organic acids from decomposing plant matter and sometimes by an acidifying effect from live plants.

Iron in solution also increases at low oxidation potentials. The oxidation potential cannot reach values low enough to produce dissolved iron as long as either oxygen or nitrate are present in the soil water. Even when conditions are right the reaction won't work at a significant rate unless the right bacteria are present to facilitate the reaction.

Biological reactions usually happen on the surface of particles in the soil. The rate of biological process in soils are elevated by the large amount of surface area per volume of soil. That surface area is created by small, irregular grains, clay minerals and porous plant debris.

In aquariums we usually suppress all of the factors that tend to make iron available in soils.

We usually encourage high oxidation potentials in aquarium substrates. Many of the same factors that prevent the oxidation potential from falling also moderates the pH of water in the substrate. We use coarse material that allows relatively free circulation; the water in the substrate is often circulated by burrowing animals; even the plants themselves can circulate water and oxygenate the substrate.

High substrate pH and oxidation potentials are probably even more prevalent when the substrate is low in organic material. Those conditions are prevalent when the substrate is new or artificially cleaned. The organic material includes organic acids that could lower the substrate pH and it is fuel for oxygen-consuming bacteria. The high oxidation potentials are even more resilient when nitrate is added to the water because the nitrate itself elevates the oxidation potential.

Moreover, course-grained, low-organic substrates provide little surface area for bacterial colonization and little surface for the exposure of iron-bearing substrate materials to water. Compared to soils there is little possibility that reactions wil produce iron in solution at a significant rate.

It should be no surprise that aquarium plants often need supplimental iron even when they are grown in a high iron substrate. We do everything we can to keep the iron in the substrate from being available to the plants, and we're pretty successful.

I'm not arguing that soil substrates are the best way around iron deficiency. I think that iron dosing -- even daily iron dosing -- is an easy and perfectly acceptable way to solve the problem.

There is also an intermediate solution. A lot of the problem arises from a lack of organic material in the substrate. It should be possible to reduce the need for added iron simply by adding organic material -- peat for instance -- to the substrate when it is set up.

Roger Miller

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_"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein_


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## Guest (Nov 18, 2003)

A thought provoking article on this interesting topic. Thanks.

I think your argument does lend support to the Walstad approach.


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## imported_locus (Feb 2, 2003)

> quote:
> 
> Originally posted by anonapersona:
> And why, when I add a bit of liquid iron, does my Sunset Hygro get redder for about 4 days, but when I add a ml or two of Seachem Excel to the same 30 gallon tank, the Sunset Hygro much redder, for almost 2 weeks?!?


The label on flourish excel states that it should be used in combination with iron based fertilisation, as it increases the plants' uptake of iron... perhaps it really works huh?


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## gpodio (Feb 4, 2004)

Roger, nice article, makes sense in many ways. Also possibly explains why I've never had the need to add liquid iron to my tanks as I use peat moss and plenty of organic waste in my substrates.

Giancarlo Podio


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## Kevin Jones (Apr 4, 2004)

I always add a little micronized iron to my organic substrates, just in case, but it would appear that this likely isn't required. 

I'm going to be setting up two tanks with commercial substrates in the coming months (probably ecocomplete) I am am wondering if peat would even be necesary for such a setup. (this is a long-time organic substrate user trying to make the transition to the commercial substrates)


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## Roger Miller (Jun 19, 2004)

It isn't necessary to use peat or soil with eco-complete or any other commercial substrate. But it might help.

After my experience with Flourite I would; 1) separate out some of the substrate and; 2) add just enough boiled peat to coat the grains then; 3) use the coated material as the lower layer in the substrate.

Roger Miller

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_"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein_


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## defdac (May 10, 2004)

.. and whats up with the "siderophore"-thingy?

http://www.engineering.ucsb.edu/Announce/siderophores.html

Awesome that it is able to reduce Fe(III) to Fe(II) by photoreactivity - the exact opposite of oxidization.

But this is perhaps just a marine phenomenon?

http://194.236.255.117/defblog/


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## Roger Miller (Jun 19, 2004)

Siderophores are biochemicals that can be produced by some plants and other organisms to help them harvest iron. They bind very strongly to iron and can take iron out of other organic complexes (maybe even from EDTA) and even from iron-bearing minerals. An iron-deficient plant would emit siderophores through its roots, then readsorb the iron-siderophore complex and extract the iron from the complex.

Siderophores produced by one plant or other organism can probably only be used by the plant that produces it. That is because the plant would need a specific enzyme to break the iron-siderophore bond. Also, siderophores can be "eaten" by bacteria, so the producing plant doesn't get back more than a fraction of what it sends out.

Not all plants produce siderophores. Other plants may pump hydrogen ions out through their roots. That lowers the pH of the soil water adjacent to the roots and makes iron more readily available.

Either mechanism (siderophores or the hydrogen ion pump) are responses to nutrient deficiency. That is, plants don't do either one until *after* they are already deficient in iron. The iron-harvesting mechanisms are expensive for the plant, as they have to divert carbon and energy to run the process and the return on their investment is low.

I reason that if the soil is saturated with water and that water is free to circulate -- as in most aquarium substrates -- the iron-harvesting mechanisms may be ineffective. That's because the plant can't get its siderophores back and because the hydrogen ion pumped by the plant is quicky diluted.

Roger Miller

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_"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein_


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## defdac (May 10, 2004)

> quote:
> 
> Siderophores produced by one plant or other organism can probably only be used by the plant that produces it. That is because the plant would need a specific enzyme to break the iron-siderophore bond.


That's not what the article suggest. They say it's a photoreaction, and somehow I feel they mean all organism benefits from the bacteria produced siderophores?

http://194.236.255.117/defblog/


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## Roger Miller (Jun 19, 2004)

The bacteria-produced siderophores are used directly by the bacteria that produce them. The siderophores may make iron more available to other organisms, but it isn't the siderophores themselves that are being used by other organisms. What other organisms use is the ferrous iron produced by decomposition of the iron-siderophore complex.

Plants as far as I know don't produce siderophores into open water; they produce them through their roots into the soil and substrate. There is no light in the substrate, so the plant-produced siderophores don't work through the same mechanism those researchers studied.

The photoreaction that the article describes is the same reaction that Fe-EDTA and other ferric-organic complexes go through in the aquarium to release ferrous iron. The siderophore's role in marine ecosystems may be new, but in aquariums the same reaction with both natural and synthetic compounds appears to be pretty well-known.

Roger Miller

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_"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein_


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## dwalstad (Apr 14, 2006)

> Originally posted by Roger Miller:
> 
> It should be no surprise that aquarium plants often need supplemental iron even when they are grown in a high iron substrate. We do everything we can to keep the iron in the substrate from being available to the plants, and we're pretty successful.
> 
> ...


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## plantbrains (Mar 11, 2003)

Side's are only found in Poaceae, grasses as I recall.

Yep, plants need very very little iron. 

But if you think you can supply all the iron need via the water column for most plants you can try, but many plants will not be very healthy.

Perhaps some plants, but there are a large group that certain have a healthy need for substrate sources. 

How do I know this?
I spent a very long time messing with a RFUG method, there was no iron in the substrate at all. Neil Frank asked what was in my substrate, I said "Not much, snail poop and the gravel is all"

This forced me to use the water column as the means which to supply the plant nutrient needs.
So I pushed the limits on the water column method. More CO2, Liquid traces, NPK etc. I had done all I could do with that, I needed to take the next step.

Roots still had access since the RFUG also pumped water by them.

RFUG made a wonderful semi control for gauging the substrates.

Very aerobic, nothing in the gravel except for bacterial films.

Most plants did dramtically well, at higher light, things became tougher.

RFUG's did pretty good with higher fish loads in Non CO2 tanks, but again, the nutrients were supplied via the water column.
Even at the hiogher fish loads/feeding, the RFUG along with the filtration quickly converted the NH4 into NO3.
RFUG are good for this conversion and high bioloads even if you add CO2.

So when I started using flourite I saw an immediate difference. So what's the deal? 
Each grain has an aerobic outside layer, with high surface area and an internal structure that allows for anaerobic regions.

The good thing about these types of gravel: decent iron content, no need for laterite etc, but if you uproot a plant, the bacteria and the reducing conditions are MAINTAINED, since each grain is it's own environment and not as dependent on it's surroundings. 

This allows for aerobic regions and anaerobic regions to be throughout the gravel and also have these regions very close together. Roots respire(no photosynthesis going on down there), that's what they do, they suck up and need O2. But they also need Mn2+, Fe2+, Zn etc.

So this provides the best of both worlds.
While at increasing light intensity, there is a greater nutrient demand, at lower levels the transport via roots is able to keep up with demand.

At higher CO2/light levels, you must add iron to the water column now.

The plant has an associated cost with transport, iron is unchelated when say Fe(ETDA) is transported across a root hair membrane, the ferric reductase leaves the ETDA behind and outside the cell(you can measure the increase in ETDA if you want to see this) then takes in the Fe as Fe2+.
All plants/algae do this. 

Plants, unlike most algae, have transport issies cell to cell etc. Iron needs to be transported where? The Shoot and the greatest demand is in the growing tip, so that's as far as possible away from one another.
So you have this Fe2+. It also needs chelated so it can be transported to the site of need.

So plants chelate the iron internally again. 

I think that as growth rates are increased, the demand exceeds the supply via the roots and you need to add some to the water column.

This is true for many nutrients in planted tanks, not just iron.

But iron is one of the must haves in the substrate no matter what method you use if you want nice growth, I was able to do it with some plants with liquid dosing alone, but the best results, results that are significant can be seen if you add a porous iron rich substrate.

Laterite does some, but it's nowhere as good as the porous substrates.

I've had 4 non CO2 tanks using Onyx(2) and flourite(2) running for a few years. 

I will say I am very impressed vs the peat or soil method + sand.

I added peat/mulm mix to the base, about 3/4" wet. Plants I had trouble with now grow well. Red plants are redder. Roots look healthier.

Iron and OM buffer eachother in terms of redox, Eh values.

If you add OM to an Iron rich substrate, the redox will be buffered for a few days/weeks around 200-300mv. If you keep adding more OM, all the iron will be reduced(and Mn). 

I add peat to add enough SLOW RELEASE OM to reduce some of the iron, but not so much nor at rate so fast that the source of Ferric iron is depleted.

This is also the concept with adding lignite/leonardite(some have been using "Fertiplant") as it slowly releases like peat humics and fulvics to reduce the Fe/Mn slowly at a balanced RATE.

If you add a ton of OM, then a some iron, yes, most will be reduced too fast.

Some folks want to add their main source of NPK via soil, this works for awhile till it's all gone and gives the tanka chance to "get going" and then rely solely, primarily on fish waste to add the rest of the NPK.

The substrate after a few months, maybe a year, mainly becomes a depot for traces, remineralization. I add the same things to each substrate, but vary the amounts depending on what method I'm using, say Non CO2 vs CO2 etc.

The OM is added for a few reasons: to get the tank off to a good start before the fish waste and bacteria settle in.
This gives the plants enough NPK via the roots etc till the fish waste are sufficent but does not add too much to cause issues. It's moderately to slightly non Labile. 
Leonardite is even less labile, more concentrated and should last longer effectively than the peat. 

The mulm is added for a labile food supply for the detrial decomposers and something for them to eat till some more detritus is built up as the tank ages and also as an inoculant, nothing like live fresh bacteria. 

So you can add mainly traces, Ca, Mg, CO3 etc and still have good results.

This is true, although slower for non CO2 tanks but also CO2 enriched tanks. They benenfit from the same processes but need more NPK than the fish can supply.

We can see this in high light tanks which will tease apart relationships faster that otherwise would be difficult to find/observe in a slow growing tank.

Then reapplying the lessons from those tanks, and applying them to non CO2 method, you have excellent results.
I'll enter a non CO2 tank in the AGA this year to prove my point. Actually a couple. 

Well off to the Blue hole research site

Regards, 
Tom Barr


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