Roles of Plant Fertilizers

Here is a nice write-up:

FERTILIZERS:

NITROGEN:
* Faster growth
* Development of an intense green color in the leaves
* Robustness issues, improving their quality
* Increased proliferation of leaves and shoots

Symptoms of a lack of nitrogen can vary but the external signs easier to observe are:
* A reduction in growth.
* A general weakening of the green colours
* A yellow beginning at the lower older leaves of the plant, and usually progresses from the apex toward the base, to cause the death of tissue and leaf drop.

PHOSPHORUS:
* Encourage an early development of the root and plant growth.
* The development of rapid and vigorous young plants.
* Increase the resistance of plants to unfavorable conditions.
* Accelerate the flowering and fruiting (interesting for those who want to multiply by sexual reproduction).

The most general characteristic of a phosphorus deficiency are:
* The plant has a reduced size. There is an obvious delay in the development and maturation.
* The green leaves are very strong and sometimes could see a purple hue in different parts of leaves, stems and branches.

POTASSIUM:
Some of the functions that the potassium in the plants are related to:
* The transformation of nitrogen in the metabolic processes.
* The production and transport of different sugars within the plant body.
* The breathing process, and so on.

The most visible symptoms of potassium deficiency in plants are:
* A reduction in growth.
* The margins of the leaves are turning yellow, rising to dry. In some cases it can also * ing a mottled appearance in the leaves.
* Appearance of weak stems, and in general there is less resistance and force throughout the plant.
* Weakness in bloom.

CALCIUM:
The lack or shortage of calcium is noted mainly in the younger parts of the plant, such as delaying their development, even paralyzing. Can be seen as the plant loses vigor and weakens the stem, showing short roots and divided. Note that a calcium deficiency also alters the absorption of other elements, since it fulfills a very important role in the functioning of the roots.

MAGNESIUM:
Magnesium is an important component of chlorophyll, which is why, when scarce, the amount of chlorophyll is reduced with the consequent disappearance of the typical green color produced by this substance (sometimes you can see a pale green, almost yellow in the tissues between the veins of the leaves). In addition, its lack has other general damages.

IRON:
It is a nutrient that is actively involved in the formation of chlorophyll and other plant functions. The shortage of iron manifests itself through the "chlorosis", ie, the leaves yellow between veins, later the whole leaf, even nerves will look glassy and brittle. Symptoms first appear on young leaves, since the iron is immobile within the plant and can not move from older leaves to new. In an aquarium, the fast-growing plants like Vallisneri, Sagittaria, Elodea densa, etc. Are affected by iron deficiency rather than the slower growing plants.

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Credit to ergarci (www.drpez.net)

 

Thanx Laure - good info, brief and to the point

 

And what type of fertilizers would those in the know suggest we use.

 

@Kuhli Loach

Research Estimative Index on the web. Most of the chemicals can be bought as dry from Dischem or similar stores. You also need to understand the ratios. You are in Pretoria, so you probably have hard water. It may be useful to know the chemical makeup of your tap water before you start. Fertilizing correctly can be very complicated. Alternatively you can just buy a pre-mixed fertilizer from any LFS and hope for the best...

Perhaps try Prof Dirk Bellstedt's fertilizer? It has been formulated for South African soft water conditions. You may have to ask him if you need anything else, since you have hard water.