66 THE AQUARIUM, OCTOBER, 1896. 
against, but even this, when the num- 
ber is large and the tanks small, will 
rapidly poison the water. But when 
the fish were carelessly handled, are 
frightened, or willfully injured, as is 
often the case, then we have, in addi- 
tion to the natural deposits, partly di- 
gested food, disgorged by the fish while 
frightened, knocked off scales and 
pieces of skinin the water. All of this 
matter is being continually stirred up by 
the motions of the fish and thus mixed 
with the water, making the latter, as 
it decomposes, more detrimental to 
them every minute. 
It is but natural that the most de- 
sirable specimens, being used to the 
very purest of water, are the first to 
succumb, soon to be followed by others. 
At best, all the fish become diseased, 
either externally or internally, and fi- 
nally die too. 
To overcome this, fish tanks are sup- 
plied with a constant stream of fresh 
water entering on one end, passing 
through the middle and leaving the 
tank again on the opposite side. To 
the casual observer this seems perfectly 
sufficient, as it creates a current just as 
we see it ina creek. But we must con- 
sider that we have a great many more 
fish over a given space of bottom than 
are found in any creek or pond con- 
tinually ; the foul air produced at the 
bottom of a fish-tank is, therefore, al- 
together out of proportion to that of a 
creek, and our aim must, therefore, not 
only be to supply fresh water to the 
tank, but also to remove the decompos- 
ing sediment from the bottom as soon 
as it appears. 
The annexed sketches will show the 
reader the various styles of in and out- 
lets, all of which have been in use with 
success by the writer. 
The tank illustrated on the upper left 
hand corner of the plate, illustrates the 
principle of forcing atmospheric air 
into the water. As the water enters 
the tank with great force through a 
very fine jet, it carries some air deep 
into the water, thus charging the same 
with oxygen. 
The foul water and the sediment col- 
lected at the bottom are carried off 
through a drain, best located in a cor- 
ner inside of the tank; this takes the 
water from near the bottom and dis- 
charges it, at water level, through the 
side of the tank. 
In localities where the water supply 
is limited, the manner shown in the 
next tank to the right is convenient. 
The foul matter is carried off at water 
level through the bottom of the tank 
by a standpipe. It is also taken from 
near the bottom. This standpipe sys- 
tem has the advantage that the water- 
level can be regulated by it, all being 
required is to slide the pipe up or down. 
A cap, in shape similar to a test tube, 
and of proper proportions to guarantee 
a free flow, reaching to within a quarter 
of an inch of the bottom, is supported 
over it either at the top of the pipe, as 
shown in the illustration, or at the bot- 
tom by putting little feet to the cap. 
For the introduction of oxygen in 
the manner shown in the next tank, a ~ 
pretty strong force of water is required. 
A strong glass tube, bent to a hook at 
its lower end, is stationed in a corner 
of the tank. In this tube a thin but 
very strong stream of water enters, 
the upper end of the tube being about 
three inches above the water level. The 
nozzle of the supply pipe is only about 
one inch above the surface and inside 
of the glass tube. The suction of this 
stream draws air into the tube which 
mixes with the water, is carried down to 
the end of the tube, and enters the 
