8 GOLDFISH VARIETIES AND 
daily, the amount depending on the degree of overcrowding. Here, again, 
a little personal judgment should come into play. 
A sprinkling pot is excellent for adding water to the aquarium. The 
small streams oxygenate the water well and do not disturb the contents 
of the aquarium. 
If running water is used, a very tiny stream will be sufficient. Fish 
used to running water when placed in still water should at first be given 
ample room. 
Plant Life. Fish live by absorbing oxygen, and they give off carbon 
dioxide as the waste product of their chemical life. Plants, under the 
influence of light, do the exact opposite, so that what is poison to one is 
life to the other. This explains why healthy plants are so desirable, and 
accounts for the phrase “balanced aquarium,” because there is a self- 
maintaining interchange established. 
Still water takes up a certain amount of oxygen from the air. The 
fishes, however, consume more oxygen than can be supplied in this 
manner, and if oxygen-liberating plants are not used the fishes become 
restless, come to the surface to breathe the air, and may finally die of 
suffocation unless the water is changed. 
The term “balanced aquarium” is not accurately descriptive, as an 
exact balance is never maintained. In practise we always endeavor to 
have the oxygenating element the more active, since any excess of oxygen 
goes off harmlessly into the air, while an excess of the poisonous carbon 
dioxide cannot be quickly taken up by the plant life. A more correct 
term might be “reciprocating aquarium.” 
Aquarium Plants. Different plants have varying powers of pro- 
ducing oxygen. It is therefore well to bear this in mind when making a 
selection for planting. Purely ornamental plants are desirable only after 
a fully sufficient quantity of the oxygen-producers have been provided. 
In the order of their oxygenating powers we would name, Anacharis, 
Vallisneria, ‘Sagittaria, Nitella, Bacopia, Fontinalis, Potamogeton, 
Ludwigia and others, which will be more fully described later. 
Light. As just stated, plants require light in order to do their work. 
Select for the aquarium a place close to a window with a good, strong 
light, preferably one where it will get about two hours of direct sun a 
day. In hot weather one should be careful not to overheat a small aqua- 
rium in the sun. A range of between 50 and 75 degrees F. is safe. 
Green water is caused by the presence of a microscopic form of vege- 
table life suspended in the water. Their growth is usually promoted by 
a combination of too much direct sunlight and a large number of fish in 
the aquarium. There are several ways of clearing the water. First change 
it, add a few fresh-water mussels, cut down the light by use of tisst.e paper 
