FAST-FLOW CLOSED-CIRCUIT MARINE AQUARIUM 



71 



of aquariums in that filter beds, tempera- 

 ture control, and large stocks of sea water 

 (an important consideration to labora- 

 tories remote from the sea) are unneces- 

 sary. The degree of success of the aquar- 

 ium here supports this conclusion. The 

 tanks in this aquarium are arranged in 

 series with a specially designed water- 

 circulating pump placed between two 

 tanks in the circuit. Thus the sea water 

 passes from the pump through one tank 

 after another and back to the pump again 

 as a continuous circulation of the same 

 water. The pump and tanks are designed 

 so as to maintain an adequate flow of 

 water; all parts of the apparatus in con- 

 tact with the sea water are of glass or 

 plastic. There is a device for producing 

 tides, technically easy in a closed system, 

 and lighting is provided for some tanks. 



The pump 



The desirable features of a sea-water 

 pump are that it should not corrode in sea 

 water nor should it have moving parts in 

 the water. Corrosion shortens the life 

 and reduces the efficiency of the pump. 

 Metals (except perhaps stainless steel) 

 may corrode and liberate ions toxic to 

 marine organisms. Moving parts are ex- 

 posed to abrasion by sand grains and may 

 damage organisms passing through them. 

 To overcome these difficulties the pump I 

 have used is an elaboration of the well- 

 known bubbling tube, and is fashioned in 

 plastics. A bubbling tube consists of a 

 vertical tube into the bottom of which air 

 is pumped; the bubbles rise to the top 

 carrying water with them. The efficiency 

 of such a tube depends on its length and 

 bore, the rate of air injection, and the head 

 of water against which it pumps. Figure 

 1 shows that a tube of about 14 -inch bore 

 with a low rate of air injection is the most 

 efficient. More water may be pumped by 

 increasing the rate of air injection, but 

 the efficiency of the tube decreases. The 



a 3 



<*. 2- 



i 



< 

 J 



i 



o 



41 



I 



OJ 0-« 0-6 , 0-8 



BORE OF BUBBLING TUBE (iNCHEs) 



1 J 1 -T- 



LENGTH OF BUBBLING TUBE (fEET) 



"1 3 , A , 



HEAD OF WATER (INCHES^ 



"IF" 



Figure 1. — Efficiency of bubbling tubes (volume 

 of water per volume of air) at stated rates of 

 air injection. At top, effect of the bore of a 

 tube (5-foot length, no head of water) ; in the 

 middle, effect of the length of a tube ( y2-inch 

 bore, no head of water) ; at bottom, effect of 

 the head of water (5-foot length, i/^-inch bore). 



efficiency of a bubbling tube also increases 

 if its length is increased. It decreases in 

 efficiency as the head of water against 

 which it pumps increases; this is not a 

 serious objection for closed-circuit aquar- 

 iums, as the head of water is never more 

 than a few inches. 



