MINIATURE CIRCULATING SYSTEMS FOR SMALL LABORATORY AQUARIUMS 49 



which operated in conjunction with the 

 protective switch. This supply was ad- 

 ministered by a float valve identical with 

 that shown in figure 3. A very nice ad- 

 justment was found possible with these 

 two float-actuated mechanisms, so that the 

 dripping from the float-valve supply be- 

 came directly proportional to the evapora- 

 tion, without at any time tripping the 

 protective cutoff float valve. On very 

 humid days it could be seen that the num- 

 ber of drops per minute was notably less 

 than on a clear dry day when evaporation 

 was high. In the case of salt-water aquar- 

 iums this device had an added important 

 application which is discussed under the 

 treatment of salt water. 



Because of the nature of the controlling 

 devices above described, it is necessary to 

 observe certain details in starting the sys- 

 tem. The levels of water in the lower 

 series of aquariums will be different when 

 the pump is not limning than when it is 

 in operation. This is mostly because the 

 drain lines of the upper series of aquar- 

 iums empty themselves into the lower 

 aquariums when the pump is stopped. 

 Therefore, the water is carried at a lower 

 level in these aquariums so that there will 

 be no overflowing when the circulation has 

 been stopped. For this reason a switch 

 should be shunted around the cutoff float 

 to be used in starting the system before the 

 operating level is reached. It will not suf- 

 fice to wedge the float into a position where 

 its switch will be closed, because its free 

 action is necessary to establish its proper 

 level of operation. After a dynamic equi- 

 librium has been achieved by adjusting 

 both the cutoff device and the density- 

 control device, the shunt switch should be 

 opened, after which the system should con- 

 trol itself. If it does not at first, very 

 obvious adjustments of either or both will 

 bring them into the proper relation. 



The diagram of the closed marine cir- 

 culating system shown in figure 8 em- 



ployed seven aquariums for holding 

 experimental fishes, only three of which 

 are shown in the illustration. Three 

 "reservoir" aquariums were used, of which 

 only two are shown. These were standard 

 commercial aquariums measuring 2 by 1 

 by 1 feet. The two smaller, used as filters, 

 measured 10 by 8 by 6 inches. The pump 

 was driven by a 1/10-horsepower motor 

 and was rated at 10.8 gallons per minute 

 at zero head. The pipe sizes are not in- 

 dicated, as they would naturally vary with 

 the needs of each system. In this one, the 

 flow was slow but sufficient at about 3 gal- 

 lons per hour through each of the seven 

 top-row aquariums. At the right of figure 

 8 the supply pipe is extended upwards for 

 some distance and with the upper end 

 open. This permits building up whatever 

 head of water is desired without subject- 

 ing the pipe to pressure greater than that 

 produced by gravity. 



Although the upper series of aquariums 

 were intended for holding fishes and the 

 lower series were regarded as treating 

 reservoirs, the latter too may be, and have 

 been, used to hold fishes, that is, all but 

 the one from which the pump draws water, 

 since the suction and turbulence here 

 would be destructive to most small fishes, 

 iterating stones and a standard aquarium 

 glass heater and thermostat comprised the 

 rest of the water-treating equipment. The 

 heater, which turned off when the water 

 reached 74° F., was sufficient to keep the 

 water throughout the system close to that 

 temperature as it was only slightly higher 

 than the normal room temperature. It 

 was found that the aerating stones made 

 it possible to permit the flow of water in 

 the lower aquariums to run through sub- 

 merged pipe outlets and thereby reduce 

 the amount of splashing and consequent 

 salt deposits. This was not found neces- 

 sary in the upper series, for each supply 

 pipe carried only one-seventh of the flow 

 in the lower pipes. 



