All green plants live by means of photosynthesis. Materials absorbed from the roots — or, in the aquarium, from the sure-rounding water — are used by the plant, together with sunlight or artificial light, to make the food the plant needs. Importantly, the plant takes in carbon dioxide and produces sugars, which it uses, and releases oxygen through tiny pores in the leaves. you can seethe process taking place in the aquarium: tiny bubbles of oxygenate produced on the leaves of certain plants in bright light. This provides a valuable source of oxygen for the fish. Further benefits that the carbon dioxide which the fish produce as a waste product is used by the plants. Moreover, the plants use the break-down products of fish wastes and decayed material.

Photosynthesis takes place only in bright light. At night, different process comes into play, by which the plant uses oxygen and releases some carbon dioxide. Supplementary aeration is therefore advisable.

Some aquarists use realistic plastic plants: these need no lights and last indefinitely, but of course have none of the valuable qualities of real plants. They are very useful, however, in giving temporary ‘instant’ plantings while the living plants are dive-loping, and can also be used with fish which would destroy or eat normal plants.

Aquarium plants are foliage plants. some grow completely submerged, in deep water, while others are bog plants which will thrive only in shallow water, or grow better part-submerged. still others are floating forms which do not root into the gravel, or which produce long floating leaves. so, as with any plant arrange-mint, careful thought is necessary to make the best of the plants you use.

Generally speaking, the principles of plant arrangement are simple. Small, low-growing plants are used in the foreground, and taller types at the back and sides. A few larger, attractive specimen plants can be put in the foreground where they can be clearly seen. Always leave some clear gravel over which fish can feed without overlooking food particles. it is advisable to leave some channels between groups of plants which increase the illusion of depth by making the viewer want to ‘look around the corner’.

Always remember that certain types of plant grow or spread very rapidly to form large clumps which can swamp less vigorous neighbours, so allow plenty of space between plantings, and be prepared to prune them heavily to maintain a tidy shape. it takes some experience to visualize the eventual appearance of a plant fit is rooted `dry’; when supported by water it will spread out and change its shape.

It is usually best to plant after filling the tank. Water plants can simply be pressed into the gravel and will take root very quickly. Special planting sticks are available, consisting of a long rod with a fork at the tip. This fork is used to grip the roots and push them into position. all the roots must be covered, or the plant will quickly become dislodged. Large plants should be weighted down with stones, at least until they have rooted wetland are secure in the gravel. some dealers sell lead wire to wraparound plant roots and hold them down, or to secure bunches of spindly-stemmed plants, but this is not a good idea: although lead itself is nearly inert, other impurities may leak out into the water.

Buy only the healthiest plants. Check the leaves carefully and remove snails or the jelly-like patches of snail eggs. Select plants from those growing in the dealer’s tank; avoid plants sold uprooted in shallow trays. many plants are just as badly affected by chilling as are fish. you can carry them home wrapped up in damp paper. Plant them as soon as possible.

Plants grow only slowly in ‘new’ aquaria, which contain few nutrients: in established tanks there is a high concentration of nitrates and other materials, and so plant growth is rapid.

Some aquarists put a layer of well washed peat, or even of sterile peat compost, beneath the gravel when starting up a new tank. This assists plant growth, but can also stimulate the growth, or overgrowth, of algae if sufficient light is present. In addition, fish digging in the bottom soon dislodge the buoyant peat or compost, creating an unsightly effect. If you do adopt this practice, remember that plants must be rooted ‘dry’, as any disturbance of the gravel in a water-filled tank releases the compost beneath.

The problem can be avoided by potting individual specimen plants in miniature plant pots containing peat, which is ’sealed in’ with a layer of gravel, and then pressing the pots into the aquarium gravel so that they are hidden. This has the additional advantage that plants can be moved with a minimum of disturbance to their roots or to other plants.

Some plants grow very rapidly and, instead of spreading out, become very long and float untidily, or grow straight up vertically out of the water. these should be pruned mercilessly, to encourage bushier growth. Remove all dead or straggly leaves or shoots to prevent decay.

Normally, the fastest-growing plants produce most oxygen and have the highest uptake of nitrates and other undesirable waste products. But, if there is insufficient light, oxygen production another useful functions of these plants stop suddenly, while slower-growing plants will continue to grow and metabolize as usual.

Material pruned from fast-growing plants can be easily used for propagation. Simply gather the cut-off tips into bunches and press them into. The gravel, securing them with a stone: the bunches will root within a week or so. This should be a regular job, with older and less healthy growth being discarded and replaced by newly rooted plants.

Some plants spread by means of runners, which either appear on the gravel surface or run along beneath the gravel; small new plants appear from time to time along the runners. these can be severed and replanted elsewhere, or left to spread into a dense clump.

It may be preferable to start out with a collection of mixed fast-and slow-growing plants. The fast-growing types, which often deteriorate after a while, can be progressively removed as the slow-growing and more desirable plants become established.

Do not neglect the potential of floating plants. certain of these have trailing roots, used by egg-scattering fish while spawning. others can be used to adjust lighting levels by providing shade. However, floating plants may quickly overgrow the water surface, and so need constant thinning-out.