TREATMENT OF FISH-CULTURAL WATERS FOR REMOVAL OF ALG^. 883 



The solution should be made by dissolving the necessary weight of sulphate 

 in a relatively small amount of water and then " making it up " to the necessary 

 volume by the addition of more water. If this volume of water is taken at the 

 beginning the solution will be too large, since the sulphate crystals add to its 

 volume. In some cases the error involved is negligible. 



SINGLE-DOSE TREATMENT. 



In the application of copper sulphate to large ponds which have a rather 

 small water flow and in which the circulation is therefore sluggish and the same 

 water remains in the pond for a considerable period, the treatment by a con- 

 tinuous flow of solution is not so effective as that by " single dose. " The reason 

 is that all waters that support fishes are slightly alkaline, and this alkalinity 

 slowly precipitates the copper from solution. The writers have tried the siphon 

 treatment twice in bass ponds with very little effect, although a much stronger 

 dilution was used than was effective in trout ponds having a much more rapid 

 circulation. In the case of these bass ponds the effect on the algx was shown 

 only about the intake to the ponds, and did not extend more than 25 or 30 feet 

 from the point where the water entered. The reason for this restriction of the 

 toxic action is taken to lie almost entirely in the prolongation of the time factor. 

 To be effective the sulphate after it is dissolved must come quickly in contact 

 with the algse. The water moves very slowly through these ponds, and during 

 this time the copper is being constantly precipitated from solution. In the 

 precipitated form it does not impregnate the water uniformly, as in the case of 

 a solution, but is gathered in minute particles which moreover do not have the 

 intimate contact with the algal filaments which is necessary in order to exert 

 a toxic action. 



In large sluggish ponds, therefore, it is better to treat them with one dose 

 of copper sulphate, the dilution being calculated to the whole volume of water 

 in the pond. In other words, a given amount of sulphate is added at one time, 

 as if the pond were a body of standing water without a current flowing through 

 it. There is no continuous addition of the sulphate. In applying this treat- 

 ment the flow may be actually cut off during the process if the fishes will endure 

 this temporary loss of water supply; or an allowance may be made for the 

 water entering during this period; or the inflow may be ignored if the pond is 

 large. With a knowledge of the actual conditions, a choice may be made 

 among these alternatives. In pond culture a constant flow of water to a 

 pond is unusual except for supplying small-mouth black bass. The other 

 species reared by pond culture," chiefly large-mouth black bass, sunfish, and 

 crappie, do not require a constant flow and it is customary merely to supply 



oSee Titcomb, Aquatic plants in pond culture, Bureau of Fisheries Document No. 643, p. 5. 



