As previously mentioned, carbon will be included in the macronutrients, even if it is not a mineral.
We will start from carbon, since it represents almost half of the dry weight of the plant.
We will talk about all the other elements following the dry weight percentage order.
Plants absorb carbon through the leaves from the carbon dioxide dissolved in the water.
In nature it comes from the decomposition of organic wastes, but the floating plants, or the plants partly above water can take CO2 directly from the 380 ppm present in the air.
Some of them can start a process called biogenic decalcification, extracting carbon from the carbonates present in the water; however thie process is long and requires a lot of energy.
The aquariums with underwater plants have very often an artificial supply of CO2.
Lack of carbon
If CO2 is not enough, we will have small leaves, the growth of the plant is consistently slowed down and we can see most of the times longer internodes.
Also the stems are most of the times smaller and delicate.
When the plant normally grows with artificial supply and this supply suddenly stops, we can see a quite quick decline of the plant; this process is much more evident than if the plant was not supplied with CO2, from the beginning of its introduction.
In particular, we will see the leaves bending down, both at the edges and at the tip.
On underwater plants we will see white deposits, due to the biogenic decalcification.
The slowing down of the growth of the plants leads to the development and growth of algae.
…especially if the aquarium is not mature enough.
Excess of carbon
It is basically impossible to damage the plant for an excess of CO2; in the worst cases it can stop its growth, due to a too low pH value that limits the absorption of other elements.
However, a value of 50 mg/L starts to be annoying for most of the fishes. Higher values can kill them.
To guarantee a good safety margin, most of the tables available, set the limit at 40 mg/L.
It is a fundamental element of amino acids, and, thus, of proteins. It is very important to convert minerals in organic tissues. The maximum absorption is at pH 7, but anyway it’s very high in the interval from pH 6 to 8.
It is absorbed in the ammoniacal and nitric form, plants cannot absorb organic nitrogen. So it is important that biochemical processes are ongoing, for instance decomposition.
Lack of nitrogen
Leaves turn to a light green color, with a tendency towards the yellow.
The problem is more visible on the older and lower part of the plant, since it tries to move the available nitrogen towards the younger leaves.
However the low degree of mobility of the nitrogen makes this a very difficult process, especially for fast growing plants.
For this reason, it is possible to find opposite experiences: some sources talk about low and old leaves, some other sources talk about the younger leaves.
On some plants, for instance Hygrophila, Alternanthera e Ludwigia, we can see a lot of adventitious roots coming out from almost all the lowest internodes, even from the ones where leaves are still attached.
In many species, not all, the leaf turns yellow, starting from the tip.
The lack of nitrogen can lead, indirectly, to the development of cyanobacteria and some kinds of algae.
Excess of nitrogen
With few exceptions, plants tolerate very high concentrations of nitrogen, in any form. On some species it is possible to see a very intense green color also on plants normally red.
Large excesses are visible most of all on the fishes, but we are talking about at least 40-50 mg/l of nitrates (NO3–) for the most common species.
In young and new aquariums, managed with too many water changes, a too long excess of nitrogen can lead to an invasion of some kinds of algae… or at least this is the common expectancy.
For many people this is just a legend, since the experiences of aquariums owners are sometimes opposite.
If the excess is in the ammoniacal form it is probable an invasion of Oedogonium, or also called filamentous algaes and this is scientifically proved.
It is considered the most representative of the mobile elements, due to the velocity with which the plant can move it.
Potassium is fundamental for the synthesis of amino acids and proteins; if it lacks, the plant cannot absorb correctly also nitrogen.
It is well absorbed from pH = 6, up to slightly alkaline values.
Except for CO2, it is the most common element missing in aquaria. Its absorption is made difficult by the presence of sodium that is, unfortunately, very common in many tap waters.
Lack of potassium
The first signal is the reduction in lateral branching to a level where they are completely absent. This happens also in species that have this characteristic.
The stem becomes thin and with a gummy consistence; we find out during pruning, that becomes more difficult without sharp scissors: it seems to cut a rubber band.
If the lack becomes long in time, the low leaves die and rot rapidly, starting form the edges, while the young ones look still good.
On the species with larger leaves, like Hygrohila corymbosa, the lack of potassium produces holes between the veinings, but always starting from the lower leaves.
This is an important detail to distinguish it from the lack of Iron, also very common.
Excess of potassium
Except for large fertilization mistakes, it is not possible to reach very high concentrations, neither for the plants, nor for the fishes.
Furthermore, a large excess can be easily detected with a conductometer.
In extreme cases you can measure more than 1000 µS/cm, however the aquaria look healthy. This is due to the fact that excesses of potassium and magnesium are very well tolerated by all organisms, including invertebrates and bacteria.
This does not mean that we can throw liters of potassium in the aquarium, but that mistakes will be most likely forgiven by the aquarium.
In even more extreme cases it is possible to see symptoms of a lack of calcium, not because the calcium is indeed not enough, but because too much potassium makes the absorption of calcium difficult. However this is the case when the concentration of potassium is at least double than the one of calcium.
It is very important for the reproduction and integrity of the cells, especially for the cellular membrane.
For this reason, many plants seem to adapt much better after planting them in hard waters, giving the impression of growing faster.
Calcium is absorbed at all values of pH common for aquaria, it becomes more difficult for pH under 6.
Lack of calcium
It is almost impossible in aquaria, due to the hardness of italians waters. However you can have problems if the GH of your water is close to 0 or if you are abusing of reverse osmotic water.
This habit is not encouraged on our forum Acquariofilia Facile, where osmotic water is simply considered as a possible method to correct the tap water that we receive at home.
The most evident symptom of calcium lack, is the deformation of the young leaves. They remain small and bended.
In many species, this symptom can be confused with a lack of copper, also very rare, but this is not a problem: the doubt is cleared by measuring the hardness of the water.
Calcium is usually the responsible for GH and KH, while copper is not part of their definition.
In some plants, the lack of calcium leads to a yellowish color of the leaves. We saw this symptom also for the lacks of nitrogen and potassium, but there are two important differences:
- The rapidity of the phenomenon. When calcium is missing the tissues die quickly and become brown.
- The position of the damaged leaves. Calcium is the most immobile of the elements, so any symptom will be only on the young leaves.
Excess of calcium
An excess is possible only with very hard waters, above 20 dGH, or with very sensible species like Cabomba aquatica.
There are no visible effects, but it is similar to a lack of magnesium (that we will see later). Calcium tends to limit its absorption at very high concentrations.
The GH test is the best way to find the reason of the symptoms, if the value is very high we can expect that calcium is too much and Magnesium is not lacking.
In addition to the 4 elements necessary for life (carbon, hydrogen, oxygen and nitrogen), magnesium is the fifth element of chlorophyll In which molecule magnesium is the central element.
It is thus the maximum responsible of photosynthesis.
It has many functions, especially related to nucleic acids and enzymatic processes.
Under pH = 6,5 the absorption is slowed down, but it goes on till pH 5,5.
Lack of magnesium
It is one of the most understandable lack: chlorosis starts from the edges of the leaf and the veinings look more evident.
The image here below shows the first stage of the lack.
If the lack is longer in time, the leaf turns yellow first on the edges then further towards the centre of the leaf. This process does not involve the veinings.
At this point, the chlorosis turns into necrosis, again from the outside to the inside. Also in this case the veinings remain green till the end.
Excess of magnesium
There are no known symptoms related to an excess of magnesium.
A very high dosage can be seen in the pH value and with a conductometer.
It is the most important element for the number of tasks it is involved into.
It influences the general growth of the plant and it allows the absorption of many other elements.
Together with sulfur, it is very important for the development of the roots; it is thus better to have enough of it during the growth of new plants.
The best absorption is at pH 7, and it is good within 6,5 and 7,5. It is the smallest interval for all the elements.
Under pH 6 the absorption is very difficult, at pH 5,5 it creates insoluble salts and it is not available anymore for any species.
Lack of phosphorus
The growth of plants slows down under any point of view: velocity, dimension of leaves, solidity of stems, development of roots…
Most of all, you can see symptoms of lacks of other elements at the same time. This leads you to think that many elements are lacking.
Actually it is the lack of phosphorus that blocks everything.
Without phosphorus also iron, sulfur and potassium are not absorbed and, as a consequence, almost all the other elements.
Excess of phosphorus
Traditionally it is associated to the formation of algae in general; actually the excess of phosphorus stimulates only the BBA (Black Brush Algae).
In not fully mature aquaria, it leads also to the formation of cyanobacteria.
However please note that this is just one of the causes, BBA and cyanobacteria require a combination of factors, among which there is phosphorus.
Furthermore, don’t forget that other kinds of algae, for example the commons Chlorococcum, are usually stimulated by the lack of phosphorus.
On the plants, the excess of phosphorus limits the absorption of zinc, in the worst cases also of iron. They appear as lacking, but actually this is not the case.
We saw that problems related to phosphorus are easily confused as lacks of other elements. Also expert aquarium owners can be fooled.
So, if you are dealing with your first aquarium, please buy the phosphorus water test. It is in fact the only case in which just observing the plants is not enough, especially if you are not yet experienced enough to think that phosphorus might be the responsible.
It is very important for the development of the roots, it is one of the main elements of some amino acids (not all, like nitrogen) and, as a consequence, of lot of proteins.
Many allelochemical substances produced by the plants are made of sulfur; without it we could not make use of these excellent natural anti-algae.
On the contrary of phosphorus, it is absorbed in a large range of pH.
There are no problems with alkaline values, not even at pH 9, where no plant could survive; for what concern acid values, it could be absorbed till almost pH 5.
Lack of sulfur
It is almost impossible to distinguish the symptoms of lack of sulfur from the ones of nitrogen because the signals are exactly the same.
However in aquaria with a lot of plants, it is very difficult that sulfur is lacking because many elements are added artificially in sulphate form.
The magnesium sulphate (epsom salt), usually used to fertilize, contains enough sulfur to bring it to slight excesses.
Furthermore, the lack of nitrogen can be easily detected with the nitrate water test. This is useful to rule nitrogen out, in case of doubt.
Excess of sulfur
In an equilibrated aquarium, sulfur is the element that most easily is present in excess. It is usually due to the artificial addition of potassium in sulphate form, very common in many commercial fertilizers. This is the reason why usually regular changes of water are suggested, even if optimal values of nitrate, phosphates and hardness are registered. The PMDD of Acquariofilia Facile uses a different approach.
On plants, the excess of sulfur can easily be seen: the young leaves die and disconnect from the stem before they reach their normal dimensions. Furthermore, sulphates can have a slight influence on the KH, even if much lower than carbonates.