TROPICAL AQUARIUM FISHES 233 
ment, but was abandoned by the writer owing to the trouble of discon- 
necting everything and washing sand every ten days, which was necessary 
owing to clogging. In top filter the cotton must be changed every two 
days, but this can be done in a few seconds. 
This arrangement both filters and aerates the water. If filtering is 
not needed, the filter can be removed and aeration will go on. 
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Fic. 179. Water CIRCULATION BY AIR PRESSURE 
Water can be raised by this method from fifteen to twenty-five inches 
above level. To secure the greater height, use 14-inch inside diameter 
tube, take plenty of drop and allow eight inches from lowest point to C. 
By this means and a little ingenuity a return fountain can be made. To 
secure a uniform flow it would require a small tank to receive the dis- 
charge from the pipe, and from this an overflow to aquarium in case the 
water supply comes too rapidly for discharge rate of fountain. 
It is not necessary to carry pipes over edge of aquarium as shown in 
diagram; they may be carried through the bottom, carrying dirty water 
directly down. The rise tube should be brought up through inside, over 
edge of filter. Short pieces of tubing long enough to reach above the 
sand and to extend an inch below the aquarium base should be used for 
passing through the slate. A very effective means of securing these in 
