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H^e "BALANCED" AQUARIUM 



A Question and an Experiment 

 J. H. POWERS 



A Well Arranged Aquarium in the Collection of H. E. Finckh 





To the aquarist the theory of the bal- 

 anced aquarium is well nigh sacred. To 

 question it is like questioning the trinity 

 among theologians. Yet much in the writ- 

 er's experience has shown that it is not 

 a dogma which can be trusted or applied 

 with confidence. 



Besides, as no doubt the readers of 

 Aquatic Life know, it has even its theo- 

 retical limitations. The animal absorbs 

 oxygen and gives off carbonic acid ; the 

 plant absorbs carbonic acid and gives off 

 oxygen. So runs the formula. But not 

 always by any means. For the animal the 

 formula holds good. But for the plant 

 only in the sunlight. Only by means of 

 the energy of the sun, acting in conjunc- 

 tion with the green coloring matter of 

 the plant and its living protoplasm, can 



photosynthesis take place, that process 

 which builds up the plant's food sub- 

 stances, employing carbon dioxide and 

 incidentally giving off oxygen. 



But place the growing plant in the 

 dark, and its nature is at once reversed. 

 It becomes an animal so far as its gaseous 

 exchanges are concerned. It needs and 

 uses oxygen and it excretes carbonic- 

 acid. 



This now being the case, the practical 

 question arises for the aquarist : what 

 is the actual condition of the balanced 

 aquarium during the night? The animal 

 population is of course deoxygenating 

 the water while supplying it with the ex- 

 cretory compound of carbon. The veg- 

 etable population of the aquarium is 

 doing exactly the same thing. But in 



