MINIATURE CIRCULATING SYSTEMS FOR SMALL LABORATORY AQUARIUMS 47 



shown in figure 8. These have been found 

 to be fully satisfactory and in several 

 years' operation have not clogged nor have 

 they become airbound. They are, how- 

 ever, not suitable for the overflow lines of 

 the upper series of aquariums. Here con- 

 stant-level siphons may be used as shown 

 in figure 2, or, preferably, a hole may be 

 drilled in the slate bottom of each aquar- 

 ium and a 1-hole rubber stopper holding 

 a glass tube inserted. Still better is the 

 installation of a hard-rubber standpipe 

 locked in place with fittings. The drilling 

 of slate is not easily accomplished and 

 there is considerable danger of cracking 

 or otherwise damaging the aquarium. 

 The manufacturers will supply aquariums 

 Avith such holes drilled on order. 



Since the supply to the aquariums of 

 this system is preferably from the top, as 

 indicated, the drain line as above de- 

 scribed may be made to draw water from 

 the bottom of an aquarium by the follow- 

 ing simple means. A tube of glass, or 



other material, of larger diameter than 

 the drain tube and as long as the depth of 

 water in the aquarium, is placed over it, 

 reaching nearly to the bottom of the 

 aquarium. Since the larger tube extends 

 above the surface, water leaving the aquar- 

 ium must enter the annular space between 

 the two tubes and pass up between them 

 to spill into the open upper end of the 

 inner tube. In addition to giving the 

 aquarium a better circulation, much de- 

 tritus is drawn up through this arrange- 

 ment and delivered automatically to the 

 filters. The outer tube, if of glass, may be 

 positioned by slipping a short piece of 

 plastic tubing on its lower end and cutting 

 various openings or notches in the plastic. 

 The area of these passages should of course 

 be at least equal to the cross-section area of 

 the inner tube. The annular space be- 

 tween the inner and outer tubes should 

 also have this much area, at least. On the 

 other hand, it is best not to make the annu- 

 lar space much larger than needed because 



Figure 8. — Arrangement of a closed circulating system suitable for small marine aquariums : A, 

 aeration outlet ; F, Alters ; H, heater and thermostat ; J, jumper ; P, pump on hanging support ; 

 8, safety cut-off switch ; V, float valve. The distilled-water supply carboy is not shown. 



