CONDITIONS OF LIGHT 
As elsewhere stated, the best light for the aquarium is either a 
northern or northeastern exposure during the summer, and a position 
where it may receive a good, unobstructed light during the winter, when a 
few hours of the morning sun would be beneficial. A fine growth of plants 
is the best indication of favorable conditions, for when the light is excessive 
at noon or during the early afternoon, it will not only cause a loss of the 
suspended oxygen by a marked increase in the temperature of the water, 
but also affect the growth of the plants by a scorching and decay of the 
leaves, and arrestment of their growth. oo little light is also detri- 
mental because plants require good light to grow. 
When the admission of light is principally on the surface of the water, 
the conditions are nearest perfect. The plants will grow vigorously and 
the animal inmates be the most comfortable. For this reason aquaria 
exposed to very strong side light should be provided with a screen for use 
during the heated portion of the day. This may be constructed of one 
or more thicknesses of violet or greenish tissue paper or cheese cloth, 
attached to a light rod, to be hung over the front pane of glass. Window 
shades partly lowered or raised from below, or the setting of the aquarium 
back from the window are also effective measures. 
Wooden tanks only admit light on the surface and should be placed 
where they will get the benefit of the morning sunlight or provided with 
awnings or other coverings that may be used when the heat of the sun is 
excessive. A fine growth of plants with floating leaves 1s the best screen 
to arrest the sunlight, and for this purpose lilies and water-poppies are 
used. 
A little experience will teach the aquariist when the conditions are the 
most favorable, and his ingenuity will devise methods of reaching the best 
results. 
WATER CONDITIONS 
The oxygen necessary to sustain the life of fishes is not that which 
forms a chemical constituent of water (H,O) but that contained in the air 
dissolved or held in suspension in the water. How considerable this is 
may be realized by looking through a glass of water heated near the boil- 
ing point. 
In streams or ponds, aeration is maintained by the action of the wind 
on the surface, but in aquaria this condition is absent, and if air is not 
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