with fertilizers. Sometimes, the amounts are so excessive as to be loxic to the aquarium plants or to ause 'algal blooms' (see page 47). Nitrates also build up naturally in an aquarium stocked with fishes as bacteria break down their waste : products (see page 19).
For an aquarium filled with mains water, therefore, an all-round plant •ertilizer is not really necessary since many of the nutrients are present in sufficient or over-abundant concentrations already. A fertilizer is ■ equired simply to 'fill the gaps' left in the composition of the mains water. As regular water changes are necessary to counteract the gradual build-up of inorganic wastes in the ;quarium, it is usually the levels of ace elements that must be made good at these times. Where rainwater used, an all-round 'physiologically ilanced' fertilizer is necessary. I ^rtilizers suitable for both instances ire widely available in liquid and tablet rm from aquarium dealers.
Below: To help new plants establish nd grow away strongly, add root tivating tablets to the gravel and nuid fertilizer to the water.
Using carbon dioxide
For many years it has been standard practice in horticulture to use carbon dioxide generators in greenhouses to boost the growth rate of both ornamental and food plants. It follows, therefore, that introducing extra carbon dioxide into well-lit and well-nourished aquariums will benefit aquarium plants in the same way by maximising the overall rate of photosynthesis.
There are several systems available for introducing carbon dioxide into aquarium water, varying in sophistication. The important point to consider is the concentration of the gas. The optimum level is 5-15mg per litre of tank water, with a maximum of 20mg/l. Avoid introducing excessive levels of carbon dioxide because of the possible detrimental effect on the fishes.
The level of carbon dioxide also affects the pH value and carbonate hardness of the water. As plants use the carbon dioxide in the water for photosynthesis - initially as C02 gas and then by extracting C02 from calcium bicarbonate - the pH value rises. Adding extra C02 causes the pH value to fall.
In their natural habitat, aquatic plants become adapted to the fluctuations in pH value that occur because of the variations in such factors as C02 level, carbonate hardness, water temperature, light intensity, water movement, concentration of plant life, etc. In the closed confines of an aquarium, it is easy to disrupt the natural balance between these factors by introducing too much C02 in a single-minded attempt to increase photosynthetic activity. But, handled carefully, there is no doubt that such techniques are beneficial in providing vital supplies of the element carbon to the plants.
The systems available for adding C02 vary from simple 'manual' ones to those linked to the lighting system (C02 is turned off when the lights turn off) and those with complex feed back arrangements involving automatic pH monitoring. Whatever system is used, it is always a good idea to test the water for C02 level, and test kits are available for this, such as Tetra Test.
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