The Aquarium 15 



of coarse gravel, so-called bird gravel, which 

 can be obtained from every bird dealer. All 

 dust and other impurities should be re- 

 moved from it by repeated washing in clean 

 water, before it is placed in the aquarium. 

 It should then be spread in such a manner as 

 to form a slanting surface, sloping, accord- 

 ing to the size of the tank, from two to four 

 inches on the higher, to from an inch to an 

 inch and a half on the lower side. By 

 turning the higher side outward and the 

 lower toward the room, it is possible to ob- 

 tain unobstructed observation of such fishes 

 as prefer the lowest and darkest corners of 

 the aquarium for their resting places. The 

 main reason for the sloping bottom is that 

 all impurities, such as excrements, remnants 

 of food and decaying parts of plants, will 

 gather on the lower side, from which they 

 can easily be removed with the mud lever, 

 — a little instrument provided for this pur- 

 pose. 



On arranging the bottom of the aquarium 



