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Re: iron and TMG etc.
Roger asked what Dupla had to say about Iron and chelators. I thought it
might also be useful to see what Allgayer & Teton have to say about
chelators.
From The Optimum Aquarium:
3.3.3 Nature as an Example
"Typical for the water in which these plants grow is that the presence of
iron in both the substrate and the actual water mass."
"In their natural habitat plants will grow in many kinds of soil including
gravel, clay substrate as well as substrate that is slimy and full of
branches, twigs and other kinds of foliage and even slough."
"What was however a common point at all the sites investigates and
substrates analyzed, was that the ground always showed a consistent and
continuous through flow of water brought about by strong bottom
circulation."
3.3.4 Substrate: A Two Way Solution
"Laterite consists of besides kaolin (terra alba) a great deal of ferric
oxide and ferric hydroxide (from 4 to 84 percent).... Iron is released under
anaerobic conditions in the ground water due to the action of organic acids
and humic acids. The same occurs in streams. Brown to rust-brown leaching,
and oozing, from such substrates can easily be observed. We have named these
leachings "nutrient springs" as they contain just about every nutrient that
can under normal conditions only dissolve with great difficulty in water,
and only as trace elements."
"Depending on the organic or the content in organic acids and humic acids of
these various waters certain quantities of iron are dissolved and released
in the water. The addition of iron rich additives has the same function in
an aquarium. Under slightly anaerobic conditions in the aquarium substrate
and also thanks to the activity of plant roots tiny amounts of iron are
dissolved and go back into solution. (This occurs under the effect of
organic acids released by the plants themselves).
3.4.6 Nutrient Supply through Nutrient Springs
"We also discovered that although the amount of water varies considerably at
different times of year...had little effect on the chemical composition of
the waters we have been analyzing."
3.4.7 Natural and Artificial Habitats
"...tropical brooks are very balanced in their composition especially since
the amount of nutrients available is evenly distributed and multifaceted."
"...in mains water, calcium and magnesium make up, on average, up to 80% of
the hardness factors, in tropical waters only 50%."
"Potassium a very important nutrient is however not to be found in mains
water. In some areas it is very limited, perhaps 3%. In the tropics however
potassium represents 17% on average."
3.4.7.2 Conclusions
"It would be a fatal error to think that the imitation in the aquarium of
"natural water" conditions would be a worthwhile pursuit."
"In natural waters with such a limited amount of nutrients the plants would
quickly absorb and exhaust the majority of them. After a short time nutrient
gaps would occur and some nutrients would be missing entirely."
"On the other hand, the stream of flowing water need only provide those
nutrients which are necessary at any given time. The aquarium, no matter how
strong the circulation still represents only a tiny amount of water. Yet in
both cases plant growth must occur according to the same laws of nature."
<discussion of the Liebig Minimum Law>
"An oversupply of nutrients can be just as damaging to plant growth as
nutrient gaps. Surplus nutrients for example can prevent the plant's
assimilation of those nutrients that are in short supply, or can lead to
formation of undesirable chemical compounds that, in turn, can cause severe
plant damage."
"In addition, many tropical plants are not amenable to nitrate as a nitrogen
source....since they have not "learned" to use this highest oxidized form of
nitrogen because they are spoiled in their native environment by ammonium,
which is much better for plants."
3.4.7.3 From Tap Water to Aquarium Water
"...nutrients that are in short supply or that are not present at all in tap
water should be added, for example, potassium."
"...some essential nutrients are produced in the aquarium itself.... These
nutrients are principally nitrate and phosphorous."
"Aquarium fertilizer must contain the entire spectrum of trace elements that
are important for plants as found in tropical stream analysis."
"Earlier we mentioned that iron, manganese and several other trace elements
are only water soluable for a short time. They oxidize in the presence of
oxygen, precipitate and are useless as plant nutrition. Immersed plants can
only assimilate these dissolved nutrients through their leaves. In tropical
streams the problem of these critical nutrients is solved by permanently
seeping nutrient sources.So the precipitated and exhausted nutrients are
continuously replenished by this ongoing fertilization."
"A good fertilizer will take on this responsibility in the aquarium as well,
by means of a chemical trick.There are chemical substances that bind and
protect certain elements so well that oxygen can not touch them and
precipitation can be largely avoided. These substances are known as
chelators or chelates."
"Ethyldiamintetra acetic acid (EDTA) is one of many nutrient carriers which
is commonly used for plant fertilization. Plants are able to take in
nutrient complexes made with EDTA, to remove the bound nutrients such as
iron et al, and to use them. A good aquarium fertilizer will contain this
and other chelators in a well balanced and carefully tested combination of
nutrients."
3.4.7.4 The Challenge of Nutrient Springs
"The discovery of nutrient springs, and the observation that certain
critical nutrients are continually replenished in plant water, led us to
certain conclusion for the aquarium. These critical nutrients are
principally iron, manganese and other trace elements which are needed by
plants only in very small quantities, but which when absent...lead to severe
plant damage. The problem with these nutrients is that they have a toxic
effect when present in large amounts, so over fertilization should be
carefully avoided. However, they also precipitate quickly during oxidation."
"The binding of these "critical nutrients" to chelators represented a
tremendous breakthrough, and an enormous step in the care of aquarium
plants."
"Recent studies have shown that there are conditions under which the supply
of these critical nutrients can not be achieved from water change to water
change, with the necessary continuity. The amount of oxygen, the pH value,
plant mass, light, fish and salt content are all factors that influence the
behavior of chelated nutrients."
"Thus, the dosage to be added to the fresh water when changing water should
be divided into daily portions."
"Another better method would be to prepare a daily or a 24 hour fertilizer,
like fish food, consisting only of the "critical" nutrients and to ad it in
doses. This should be combined with iron measurements becasue all trace
elements behave like iron towards oxygen, pH value and other factors that
determine their use and precipitation. An Fe content of 0.1 mg per liter is
desirable, whereby it is important to remember that small traces of iron are
available even in the avsence of light. We believe that higher levels of
iron such as 1.0 or even 2.0 mg per liter which is commonly suggested are
too high and quite unnatural."
<finis>
From The Complete Book of Aquarium Plants, Allgayer & Teton:
[anything in square brackets is me......]
Trace Elements
"The term "trace elements" is applied to all substances in low
concentrations needed for life and plant growth."
Assimilation
"In the earth, plants draw trace elements through their roots; while in
water, special organs (hydropods) situated on leaves are used by plants for
assimilation. Before they can be assimilated in water, trace elements will
need to be there in an ionized and soluable form, and the ionized form will
have to be right for the plants."
"...take the case of iron (Fe)... it is found in two ionized forms: Fe++ -
ferrous iron, and Fe+++ - ferric iron. Only the first form can be
assimilated by plants, and only if it is linked to an organic compound which
can maintain it in soluable form. Organic molecules, which in this state
release iron and other metals such as magnesium or manganese, are known as
chelators."
Chelators
"These are complex organic molecules, capable of binding with metal ions or
certain proteins, to render them soluable and acceptable to plants. The
compounds are found naturally in the aquarium, especially in the substratum.
Often, they are humic acids which result from argillo-humic compounds. Some
experts recommend filtering be carried out with material rich in humic acid
such as turf so as to incorporate the clay or agrillo-humic compound in the
tank. Unfortunately, these substances deteriorate quickly."
"The best solution is to artificially chelate trace elements, with a
chelator systhesis. EDTA is the most popular with aquarium owners and
hydroculturists.....only the disodium type should be used."
Iron deficiency
"Regular water changes ensure a sufficient supply of most trace elements,
but cannot meet the plant's need for iron. In very hard water, calcium and
magnesium are chelated first, and the iron is ignored. First, extra iron
should be added, and second, extra chelators. There is absolutely no point
in introducing iron in solid form, as nails or granules."
Iron additives/chelators
"Hard water generally has an average [iron] concentration of 2.0
mg/L........where iron is naturally present in a concentration higher than
1.5 mg/L, there will be no need to supplement it. But this concentration
could be raised to 2.5-3.0 mg/L, accompanied by the chelator EDTA." [this
all assumes that you are adding the chelator SEPARATELY]
"Bivalent iron can be added....in various forms: as tetrahydrous chloride Fe
(C12 4H2O); as dihydrous gluconate C12H22FeO14 2H2O; or as hydrous sulphate
FeSO4H2O accompanied by a chelator. The amount of EDTA required will be
slightly optimized, in keeping with the amount needed for iron alone."
Excess chelators
"If the trace element/EDTAproportions are not right, the plants will suffer
physiological disturbances. An overdose of EDTA [again, this is referring to
the practice of dosing the chelator SEPARETLY] implies that a certain amount
of chelator in the aquarium has not been combined. It will do so in a
preferred order: calcium, magnesium, and manganese, and finally, bivalent
iron. With an overdose of EDTA, chelation continues and it can happen that
large amounts of trace elements , in the form of various metallic ions, will
be caught up. and this applies not only to metallic ions in the water and
substratum, but also those stored in plant tissue. It is possible,
therefore, for iron oxides which are stored in the aquarium to be suddently
mobilized by excess EDTA. Bivalent iron, in excess can supersede other trace
elements important to vital plant proceses.... The result will be a
deficiency caused by an imbalance betweenthe various trace elements. These
problems will not arise if the chelates-chelators proportion is strictly
observed, and a close check kept on iron content."
"Your should also guard against adding chelates very suddently to an area
which has been chronically deficint.. Overdosing will not revive stunted
plants..... As we have seen, it will merely produce a negative effect, and
sudden chelate treatment can cause under-nourished plants to suffer a kind
of alimentary collapse, particularly those of the genus Cryptocoryne."
"Aquarium chelation should be carried out cautiously after due consideration
of the energy balance. In a newly-installed tank, the dose is calculated on
total contents and thereafter it should be measured with weekly or monthly
water changes."
"Fertilizers and chelates which are suitable for garden and indoor plants
will not be appropriate for aquatic plants. Apart from iron, these chemical
additives contain large amounts of nitrates, phosphoric anhydride or
potassium oxide. These substances are too rich for an aquatic environment in
which they are already well represented."
Measuring Iron
"The chelation ratio of EDTA to trace elements is molecule to molecule. The
molecular mass of products used should be known. Remember that the molecular
mass corresponds to the mass of N molecules of any one product [N=6.023 X 10
to the 23rd power]. Molecular masses of the following products are:
EDTA (Titriplex III) M = 372.24 g
Iron Sulphate (Fe SO4) M = 151.91 g
Iron Chloride (Fe Cl4, 2H2O) M = 198.81 g
Iron Gluconate (C12H22FeO12, 2H2O) M = 482.18 g
This amount would be sufficient for an aquarium of 1,000 L (220 gallons)
with a proportional amount of EDTA. Unfortunately, some unstable factors,
like pH or a preferential fixation order conditional on EDTA, can disturb
iron chelation. Preferential constants mean that first the chelator combines
with magnesium, then calcium. In principal, chelation in hard water will
mostly affect carbonate hardness elements, such as calcium and magnesium."
<finis>
James Purchase
Toronto