MARINE AQUARIUM PROCEDURES AND TECHNIQUES 



65 



rougher. Another intervening factor is 

 the action of the fauna which modifies the 

 permeability of the ground by burrowing 

 corridors. The fauna which consumes 

 oxygen favors the circulation of water in 

 the submerged sand. These considera- 

 tions have permitted us to use substrata 

 of sand of considerable thickness, capable 

 of accommodating a rich fauna. We have 

 built this tank with the thought in mind 

 that an adaptation period is required dur- 

 ing which the fauna and the flora become 

 settled and establish a certain equilibrium ; 

 thereafter, the artificial balancing mecha- 

 nism (water current, etc.) can be reduced 

 considerably, without any important 

 change of the biotope. 



The scheme of an experimental sand 

 tank is shown in figure 9. The water 

 comes in at i, through the large vertical 

 pipe which is open at 2 and 3. The water 

 reaches the bottom of the tank directly, 

 flows freely between the pebbles and the 

 various shells, passes through a nylon or 

 fiberglass screen and filters through the 

 sand layer 6. The sheet of water 7 fl,ows 

 off through the siphon 8. 



The volume of water which arrives at 1 

 does not flow off easily through the sand 

 layer. When the water level in the large 

 pipe rises the pressure in that pipe in- 

 creases. That pressure must not be too 

 high because the water would immediately 

 pour forth violently from the sand, in the 

 form of a "spring." It is easy to deter- 

 mine the optimum pressure. In practice, 

 the height of the water column above the 

 level of the tank {5) must amount to ap- 

 proximately one-fourth the depth of the 

 sand. It is possible to make an opening 

 of any size in the large pipe, preferably 

 at that level. This is what we have done 

 in the case of the usual breeding tanks. 

 We have now begun, however, to make ex- 

 perimental tanks that have an opening If. 

 at a lower level than that of the water in 

 the aquarium. To that opening, we have 



Figure 9. — Scheme of a sand tank : 5, height of 

 the water determining the pressure required 

 for irrigation of the sand. 



attached a bent tube which is open at 3. 

 By making that tube rotate around 4, the 

 opening 3 may now be brought to the 

 level desired. By means of devices of this 

 type we obtained our first data concern- 

 ing the equilibrium of aquariums with 

 sand bottoms. When the tank has oper- 

 ated in that w^ay for a certain time, the 

 sediment settles somewhat, the bottom be- 

 comes clogged, and the amount of water 

 that will effectively pass through the sand 

 on its way from the large pipe is reduced 

 gradually. One may then remove the 

 bent tube and, thereby, suppress almost 

 completely the irrigation coming from the 

 large pipe. The irrigation of the sand 

 will then continue to be taken care of al- 

 most exclusively by the fauna that has been 

 installed in the sandy substratum, and no 

 symptoms of anaerobiosis will appear. 



