Caring For Plants

Plants need light, mineral salts (fertilizer), and carbon dioxide (CO2) to grow, and their survival and reproduction depends on the right proportions of these elements. A fishkeeper also needs to be an aquatic gardener and have "green fingers" to cultivate his or her live decor.

You must respect the needs of plants to obtain optimal growth and reproduction.

Plantshave an overwhelming need for light, whether natural or artificial, to grow and produce oxygen, once they haveabsorbed carbondioxide

You must respect the needs of plants to obtain optimal growth and reproduction.


Aquatic plants are in general very sensitive to the water quality. Although some plants, such as the floating fern, are easy to keep, and seem indifferent to the quality of the water, others require water that is soft and acid or, alternatively, alkaline and hard, and will only flourish in water that is adapted to their specific needs.


Aquarium plants usually need strong lighting, produced by special fluorescent tubes for 12 or 13 hours a day. For information concerning lighting see page 226.

If the lighting is deficient in either quality or quantity, the plants will turn yellow and eventually die.

Carbon dioxide (CO2), oxygen (O2), and photosynthesis

Like all living beings, plants are continuously respiring. They consume oxygen and expel carbon dioxide, thereby affecting the oxygenation of the water, both in a natural setting and an aquarium. By contrast, in reaction to light - therefore only by day - they absorb the carbon dioxide from fish respiration and produce oxygen: it is this photosynthesis that enables them to grow. This phenomenon has a beneficial effect on the equilibrium of the aquarium, as it results in the production of more oxygen than the plant consumes in its respiration. There may be slight variations in the oxygen levels from day to night, with the minimum levels being reached in the last third of the night. An aquarist (preferably an insomniac!) can verify this by measuring the pH every hour in a cycle of 24 hours (see diagram on page 14). An increase in the water's oxygen level pushes up the pH, while the production of CO2 at night acidifies the water and the pH goes down.


Magnesium is an important element, as it makes up part of the chlorophyll pigment that absorbs light. Iron plays a role in the chemical reactions of photosynthesis. If plants are deficient in iron, their growth slows down and they turn yellow; specialists refer to this as chlorosis - a condition also seen in agriculture.

This phenomenon, which is only really visible in heavily planted and densely populated aquariums, rarely entails any problems for fish.


When an aquarium is put into operation, the bed and the water contain mineral salts. These gradually run out and the plants are therefore in danger of mineral deficiency. Faced with this situation, an aquarist has three options:

- regularly change part of the water (generally 10% of the volume per week), to obtain "new" water containing salts;

- add liquid fertilizers specially designed for aquatic plants;

- add solid fertilizers, in the form of sustained-release mineral salt capsules placed at the base of the plants.

You can also make a solid fertilizer at home, based on clay. Knead it, form small balls, then have them soak up liquid fertilizer. Placed at the base of plants, these balls gradually release their nutrients.

Mineral salts

This name covers all the substances needed for the growth of aquarium plants. They are in fact the equivalent of the fertilizers that are used in agriculture, or for house plants.

Plants' needs vary according to the substance: some are only required in tiny amounts (metals, for example) but they must be constantly available. Mineral salts are absorbed by the roots and leaves in truly aquatic plants, and by the roots in amphibian plants.

In the natural environment, some aquatic areas are considered fertile, as the renewal of the water and the equilibrium of the natural cycles provide sufficient amounts of mineral salts for plants to prosper. Those regions lacking these vital elements are characterized by sparse vegetation, or none at all. In an aquarium, which is a self-contained environment, the water and the bed contain mineral salts that will gradually run out, at a rate determined by the quantity of the vegetation. You must therefore make plans to reinforce the mineral salt level on a regular basis, as you would for


1. Choose plants suited to aquarium water.

2. Choose hardy species, some rapid growers and other slower.

3. Satisfy their needs, especially as regards special lighting.

4. Check the supply of nutrients.

5. Do not hesitate to ask for advice, from your aquarium store owner or from clubs and associations.

There is usually enough carbon dioxide in the water, but it can sometimes be deficient, even in a tank that is profusely planted and well lit. If this occurs, the carbon dioxide that has been trapped by the bicarbonates is used in its turn: the pH often rises above 7.5, sometimes even up to 8, in fresh water, and the calcium forms a fine layer on leafy plants and "suffocates" them. Deposits can also be seen on the glass panes, at water level. Carbon dioxide diffusers are available in the aquarium trade to remedy this problem. You must also bear in mind that aeration and stirring of the water, which contribute to its oxygenation, help expel the CO2

dissolved in the water MM»p into the atmosphere. This ay means that excessive stirring can sometimes have dire consequences for plants.

Nowadaysspecialist aquariumstores stock equipment designed to supply plants with the CO2 they need. •

Nowadaysspecialist aquariumstores stock equipment designed to supply plants with the CO2 they need. •

house plants. Some aquarists provide, from the very beginning, an enriched soil that will gradually release these mineral salts. This is particularly useful when


Nitrogen, contained in nitrates.

- Phosphorus, contained in phosphates.

- Potassium, which is a component of other salts.

A few other substances are also needed, sometimes in very small quantities:

- Metals, such as iron and magnesium (see page 196);

- Vitamins.

extensive planting is envisaged for the aquarium (in the case of a Dutch aquarium, for example - see page 33).

sible to find veritable "aquatic horticultur-alists" who obtain astonishing results.

How do you know if your plants have a growth problem?

A plant lacking any of the elements it needs to live turns yellow or brown and rapidly dies. The leaves get covered with a fine layer of filamentous algae and eventually fall off. However, in some species it is not easy to tell when the growth process is slowing down.

Vegetationcan thrive in an


Many aquarists treat plants as mere deco-

aquanum,if it: is rative elements; others cultivate them in provided with , , good lighting and the same way as they raise fish: they make nutrient salts. • them grow and even reproduce. It is pos-

nutrient salts. • them grow and even reproduce. It is pos-

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