Looking at many sources in bibliography, there are different definitions of «oligoelements», «micronutrients» and «trace elements».

For someone these are synonyms, for others only the first two, or the last two… and someone proposes an internal subdivision: defining all of them as oligoelements but divided in two groups with other two names…

In this article, for us it is important to talk about lackings and excesses of elements. So we will ignore all that elements that have no effect in aquaria.
We will talk about: iron, chlorine, manganese, boron, zinc, molybdenum and copper.


It is not an element in the composition of chlorophyll, but it is essential for its formation.
Also other pigments depend on Iron, for this reason it is very requested by red plants.
It is part also of the synthesys of many allelochemical substances. This discovery leads us to consider Iron as an enemy for algae, even if not directly, while in the past it was considered a responsible for algae development.

Iron is very well absorbed with pH lower than 6. For this reason, chelates are used in fertilization. These organic molecules make sure that iron remain in solution.

Lack of iron

The young leaves are the most affected, because they are more exposed to light.
The veinings keep their original color, while the tissues turn yellow.
It sounds similar to the lack of Magnesium, but there are differences that help distinguish the two cases.

First of all, magnesium is a mobile element, the plant can move it. Until there is a small quantity of element available the new leaves present no signs.

If iron is missing, on the other hand, we can see it on the new leaves that grow deformed and bended:

Lack of iron
Lack of iron

This symptom is related to the initial stage of the lack, since the plant stops soon growing and it does not produce any new leaves.

For long lasting shortages, in case of lack of magnesium we can see necrosis starting from the edges and growing towards the centre. When Iron is missing you can see holes in between the veinings:

Lack of iron
Lack of iron

Also in this case the problem is mostly related to the upper leaves, since more exposed to light.

Excess of iron

You can read everywhere that it slows down the absorption of manganese and that you can see the related lacking symptoms; actually this happens with very high concentrations of Iron.

In the meantime, we have a quite clear signal: leaves turn to red, starting from the tips, also on green plants.

Excess of iron on a Bacopa
Excess of iron on a Bacopa

Iron can collect in the water in large quantities without any problem for the fishes. However crustaceans are quite sensible to excesses.


It adjusts the opening of the stoma, small porosities on the lower side of the leaf. It is thus very important for water plants, since the leaves absorb not only CO2 but many other elements.

It is absorbed at any value of pH of interest for aquaria.

Lack of chlorine

According to a recent hypothesis, the virus causing the appearance of the Hygrophila «Rosanervig»…

Hygrophila polysperma "Rosanervig"
Hygrophila polysperma “Rosanervig”

…acts on the assumption of chlorine.

The effect of this lack is in fact the loss of color of the veinings.
However, unless some very special event, this never happens in aquaria. Also not considering the artificially introduced chlorine, our waters are normally rich with Chlorine. The quantities involved are larger than the needs of the plants, so that on fertilizers for gardening we can often find the indication of low chlorine content.

Excess of chlorine

It is normal to have also large excesses of chlorine. No relevant symptoms were ever noticed.



It is involved, as Iron, in the formation of chlorophyll and other photosynthetic pigments. It is important for the enzymatic activity, second only to potassium.

Also manganese requires a certain level of acidity to be absorbed, it extends up to 6,5 pH.

Lack of manganese

Edges turn yellow and tissues die soon. Necrosis proceed towards the centre of the leaf in case the lack is long in time.

Lack of manganese
Lack of manganese

It sounds very similar to the lack of magnesium, but there is a difference: in case of manganese, the necrosis invades the whole leaf, also the veinings. On some species, the leaf starts turning yellow right from the veinings.

Excess of manganese

The plant shows the symptoms of lack of iron even if iron is abundant. This is due to manganese that stops iron absorption.


It is important in the absorption of carbohydrates but also in the formation of the cell wall.
ts effect on the growth hormones makes it essential for opposite zones of the plant: roots and new leaves.

It is well absorbed at any pH value lower than 7, otherwise the absorption drops quickly. Plants need it especially during the flowering phase. In open aquaria, with emerged plants, boron must be added generously.

Lack of boron

The plant slows down, it has difficulty in creating new leaves. The new ones bend the edges and get a weird color.

Probable lack of boron on Rotala macrandra
Probable lack of boron on Rotala macrandra

Excess of boron

It can make the absorption of iron difficult, the leaves turn yellow cause chlorophyll is not produced anymore.
However it is impossible to have such large excesses in aquaria, except in cases of serious mistakes.


It takes part in the production of chlorophyll, even if it is not as important as iron and manganese. Like boron, it is important for the growth hormones.

Its absorption is in the same range as boron, under pH = 7, above this value the absorption decreases gradually.

Lack of zinc

The tissues between the veinings turn yellow, differently from the lack of iron and magnesium, it looks like it never leads to necrosis.

Lack of iron?... Or magnesium?... Or zinc?
Lack of iron?… Or magnesium?… Or zinc?

It is probably due to the very low concentrations requested by the plants. Normal commercial fertilizers and PMDD have more than enough zinc.

Excess of zinc

Same as for boron.
It is impossible to reach problematic concentrations.


Its effect on the enzymatic activity makes it necessary for the trasformation of nitrates in ammoniacal nitrogen, the form that the plants absorb.

Molibdenum is best absorbed at pH above 7, in any case not below 6. It is not a big problem, aquaria are never so acid, or at least not for a long period of time.

Lack of molibdenum

The lack of molibdenum presents the symptoms of a lack of nitrogen, already described.

Lack of nitrogen
Lack of nitrogen

The plant needs a very small amount of molibdenum, so it is very difficult that this happens; if it happens it is sufficient to measure nitrates to understand the element that is lacking.
In fact, if nitrates are high it means that nitrogen is sufficient, however the plant cannot absorb it due to the lack of molibdenum.

Excess of molibdenum

There is no literature about this problem in aquaria. No fertilizers create an excess of molibdenum, just because the quantity needed is really small.


It has an antiparasitic effect that makes it very common in many fertilizers for gardens.
In aquaria is still used as anti algae in some commercial products. This often creates some side effects.

If concentration is of few ppm it is useful for the transportation of carbohydrates and in the syntesis of proteins.

The absorption is best with acid pH, but it can be partly absorbed up to pH 8,5.

Lack of copper

The small quantities requested are in the fish foods, in tap water and in some fertilizers.
So it is very unusual that it must be added.

However, if it happens, the clearest symptom is the bending of the edges of the leaves towards the inner part.

Lack of copper
1) Lack of copper; 2) Initial phase; 3) Advanced phase

Some plants tend to lose their color, similarly as for a lack of iron.
On very fast growing plants, if copper is lacking, the new leaves are deformed as if calcium is lacking.
These problems are present especially if other elements are present in balanced quantities and thus, if the plants tend to grow fast.

Excess of Copper

If regularly introduced artificially, it is easy to have an excess.
If it happens, it is the most severe excess that you can have in your aquarium: chlorophyll is quickly destroyed and this leads to the death of all the plants.

In the past it was just copper that leads to the failure of some PMDD, made with gardening fertilizers that contained too much of it.
It is sufficient to have 0,03 mg/L to make copper a real venom, both for the vegetation and for invertebrates and micro organisms.


Many of the images of this article were made by the users of Acquariofilia Facile, others are public or under Creative Commons license.
In any case, I would like to thank the authors that made the comprehension of this article easier.

I would like to repeat one more time that any information here must be interpreted with elasticity. Please do not hesitate to visit our forum and discuss about your plants’ problems with usand other users.

Acquariofilia Facile would like to thank personally our user Chry for the translations of this article. The staff only has corrected any typing errors, without affecting the structure of the user-made translation.

We hope to be able to spread our articles to an ever-larger audience, thanks to the collaboration of the forum.

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