TREATMENT OF FISH-CULTURAL WATERS FOR REMOVAL OF ALG^. 88 1 



In a case where the writers appHed both methods of estimating flow, the 

 lowering and refiUing a pond and measurement of speed in a closed pipe, 1,127 

 gallons per minute were obtained as the result by each method. The exact 

 agreement was a mere coincidence, since these methods can not be presumed to 

 have the degree of accuracy implied, but it indicates that flow may be esti- 

 mated in a practical way by these means. 



The more accurately the flow is known the more rapidly and confidently may 

 the treatment proceed. But it is not necessary to refrain from the treatment 

 even if no measurement of flow is possible. Any person practiced in esti- 

 mating water flow with some accuracy by the eye may make a minimum esti- 

 mate. Using this as a basis, a dilution of copper sulphate, much weaker 

 than the susceptibility experiments indicate, may be assumed as safe. The 

 treatment should then be cautiously begun with constant watching of the trout 

 and testing them with food. As a fatal strength of copper is approached 

 they will be thrown "off their feed." While they remain unaffected the 

 strength may be gradually increased until the desired effect is obtained. 



3. DETERMINATION OF VOLUME, STRENGTH, AND RATE OF INFLOWING SOLUTION. 



The desired dilution and the volume of water flow per minute are now known. 

 The volume of copper sulphate solution, the weight of copper sulphate crystals 

 which are to be dissolved to make this solution, and the volume of flow per minute 

 from the siphon to produce the desired dilution, are to be determined. These 

 three may be mutually arranged in the way which is most convenient. Since it 

 is less easy to change the siphon flow, or to make a siphon which will have 

 exactly a given and predetermined flow, it is better to adjust the volume of 

 solution and weight of sulphate to the fixed siphon flow whatever it is found 

 to be after setting up and starting. The siphon may be made to deliver small 

 amounts, even drop by drop, if desired. A flow of 20 c. c. to 100 c. c. or more 

 per minute eovers most cases. The flow should not be so large that renewal of 

 the solution is too often required. If the siphon flow first hit upon is not within 

 reasonable limits it may be increased by lengthening the outer arm or by 

 increasing the diameter of the orifice in the siphon nozzle. It may be decreased 

 by shortening the outer arm. 



Having now the siphon flow determined, as well as the dilution and the 

 water flow, the volume of the sulphate solution and the weight of sulphate to be 

 dissolved for one filling of the container of the solution remain to be fixed. It 

 will be natural to approximately fill the container. The volume is thus fixed 

 and the weight of sulphate must be adjusted with reference to it. On the other 

 hand, if only a given weight of sulphate is available, too small an amount to make 



