94. THE MARINE AQUARIUM. 
management; every new supply is a witness of the 
aquarian’s lack of skill, as Mr. Lloyd wisely says, ‘“ pro- 
perly managed, the water and other contents of an 
Aquarium may be kept unchanged for periods indefinitely 
prolonged.” For the sake of aquarian science, I do im- 
plore the student to surmount any and every difficulty, 
rather than own the weakness implied by changing the 
water. 
Aeration is frequently referred to in works on the 
Aquarium. It is at variance with the self-sustaining 
theory, and there is something wrong where it is wanted. 
If the tank is stocked before the plants are well estab- 
lished, or if overstocked with a crowd of animal life, or 
if sulphuretted hydrogen be produced and make its 
presence manifest to the nose, then aeration may be 
necessary. A cup or jug may be used to dip water from 
the surface, and pour it back again from a height in a 
thin stream. Or a filter may be placed over the tank and 
filled from the surface, and the water allowed to drip back. 
But the most efficient instrument is a common syringe. 
This is simply to be charged at the surface, and dis- 
charged again with some force, so as to send a stream 
of oxygenised water deep into the tank. The process 
should be repeated for a quarter of an hour at least. 
Filter.—A bee glass or a common flower-pot may soon 
be made into a filter. Thrust a piece of sponge into the 
hole in the bottom, and upon it lay a stratum of washed 
sand and powdered charcoal. Pass the water through it, and 
it will be purified, and saturated with oxygen at one and 
the same time. With the river-tank, the simplest way of 
