[...]... water aquariums, where the water temperature can range from 5 to 25°C; - tropical aquariums, with either fresh or sea water These cover the areas lying roughly between the tropic of Cancer, to the north of the equator, and the tropic of Capricorn, to the south, where the water temperature varies by only a few degrees throughout the whole year TEMPERATE WATER AQUARIUMS These are not heated, and ideally the. .. them more easily; - there is less risk of disease, particularly in the fishes' branchiae; - there is little sedimentation on the base of the tank, reducing both the possibility of any warping due to excessive weight and the decomposition of organic matter In an aquarium, the situation is different Some fish partly feed on plants, but most of them are fed by the aquarist; sometimes there is a surplus... adjustments to be made to the pH, but there are other ways of modifying it • If the pH is too high - the water can be diluted with another more acid water; - the stirring of the water can be reduced Carbon dioxide is eliminated less quickly and remains in the water to acidify it Be careful, because decreasing the stirring also lowers the oxygenation; - the water from the aquarium can be filtered over peat,... base of the food chain, they also take part in the nitrogen cycle 19 WATER, A HAVEN FOR LIFE Bacteria in the nitrogen cycle Rarely found in open water (around 1% of the total count), bacteria colonize essentially the floor and the decor They feed on nitrogenous compounds in the water, extracting the oxygen from them.When an aquarium is brought into use, bacterial colonization of the environment is a slow... Adjusting the density • The density is too high Part of the water is siphoned off - this can be stored for later use - and the softest water available is added, taking care to measure the density When the water level of a marine aquarium goes down because of evaporation, it is not the sea water which is evaporating but the fresh water, and it is therefore the latter which must be added to make up the level... and 9 These extreme values are rarely found in an aquarium, where the pH ranges from 6 to 8 according to the type of water, and usually lies between 6.5 and 7.5 In aquariums, the term acid water corresponds to a pH between 6 and 6.8, while alkaline water Maximum oxygen content of water as a function of temperature • T°C mg/lrter 15 16 17 18 19 20 21 22 23 24 25 26 27 28 10 .1 9.9 9.7 9.5 9.3 9 .1 8.9... derived from humus These tanks house other species of Characins, or Cichlids, particularly the famous angelfish and discus The water is very soft in both these types of aquarium • African aquariums A biotope of a West African river can be reconstructed in an aquarium The water, which must be well-filtered, is neutral and quite soft The fish will include the Congolese tetra, one of the rare . of temperature • T°C 15 16 17 18 19 20 21 22 23 24 25 26 27 28 mg/lrter 10 .1 9.9 9.7 9.5 9.3 9 .1 8.9 8.7 8.6 8.4 8.3 8 .1 7.9 7.8 13 WATER, A HAVEN FOR. Coordination: Nadja Bremse-Koob Production: Ursula Schumer Printed in Italy by STIGE - Turin ISBN 3-8 29 0 -1 73 6-7 10 9876543 21