THE FRESHWATER AQUARIUM AND ITS MAINTENANCE 



also first applied the term " aquarium " to fish tanks, it having previously 

 been used by the botanists to designate aquatic plant receptacles. 



The Properly Conditioned or Balanced Aquarium. "When 

 properly arranged, its maintenance is very simple, but the governing prin- 

 ciples of a balanced aquarium are not always understood. It is not real- 

 ized that when the relations of plant to animal life are correctly propor- 

 tioned, the aquarium is virtually self-sustaining or balanced, and the water 

 need only be changed at long intervals, often of a year or more. 



Plants in their growth liberate oxygen and take up the carbon-oxide 

 and dioxide given off by the living creatures; the latter, in their turn re- 

 quire the liberated oxygen, which is either in suspension or dissolved in 

 the water, to maintain their existence. Hence, if the plants and animals 

 are properly balanced, the quality of the water remains fixed, and only 

 becomes vitiated after a long period through the presence of other gases 

 generated by the excrement of the animals and the decomposition pro- 

 duced by the general decay of the plants, of food, and other organic sub- 

 tances. Oxygen is absorbed in considerable quantity by the breathing 

 organs of the living inmates, for the oxidation of waste carbonaceous 

 matter, thereby producing carbonic acid gas. This, during the daytime, 

 is absorbed by the plants, the contained carbon being required to add to 

 the solid structure of the plants, and the oxygen is set free in the water. 

 Thus the double action of animals and plants maintains an almost perfect 

 balance, as the animals diminish the proportion of oxygen and add to the 

 quantity of carbonic acid gas, and the plants increase the oxygen and di- 

 minish the carbonic acid gas. 



The fishes, however, consume more oxygen than still water takes up 

 from the air, and if oxygen-liberating plants are not introduced into the 

 aquarium, they suffer from the lack thereof, become restless, come to the 

 surface to breathe the air, and may finally die of asphyxiation. 



It must not, however, be taken that an exact balance is ever attained, 

 and it is better to have a preponderance of the oxygenating element,, re- 

 stricting the animal life to that which will live corofortably in the existing 

 environment, and that the nearer these conditions are approached the 

 better the inhabitants will thrive and the less often the .water need be 

 changed. 



Aquarium Plants. Not all aquatic plants are equally good gener- 

 ators of oxygen and some Information is requisite to make a selection of 

 those which best fulfil this necessary purpose. There are quite a number 

 of readily obtainable plants which perform this function, many of them 

 native and others to be had of dealers. These are, in the order of their 



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