Mr. Warrington kept for a whole year twelve gallons of water in a state
of admirably balanced purity by the following beautiful action:
In the tank, or aquarium, were two gold fish, six water-snails, and
two or three specimens of that elegant aquatic plant _Valisperia
sporalis_, which, before the introduction of the water-snails, by
its decayed leaves caused a growth of slimy mucus, and made the
water turbid and likely to destroy both plants and fish. But under
the improved arrangement the slime, as fast as it was engendered,
was consumed by the water-snails, which reproduced it in the shape
of young snails, which furnished a succulent food to the fish.
Meanwhile the _Valisperia_ plants absorbed the carbonic acid
exhaled by the respiration of their companions, fixing the carbon
in their growing stems and luxuriant blossoms, and refreshing
the oxygen (during sunshine in visible little streams) for the
respiration of the snails and the fish. The spectacle of perfect
equilibrium thus simply maintained between animal, vegetable, and
inorganic activity, was strikingly beautiful; and such means might
possibly hereafter be made available on a large scale for keeping
tanked water sweet and clean.--_Quarterly Review_, 1850.