LD 50's for four sources of water supply were 0.6 p. p.m. at TH 

 15 p. p.m.; 8 p. p.m. at TH 68 p. p.m.; 10 p. p.m. at TH 100 p. p.m.; 

 45 p. p.m. at TH 132 p. p.m. Total alkalinities in the four waters 

 were 18.7, 166, 245, and 1544 p. p.m., respectively. Therefore, 

 copper sulfate treatments of soft— water hatchery ponds should be 

 undertaken with caution. 



Muskgrass ( Chara ) , a form of algae attached to the bottom, 

 often invades hardwater ponds, rendering them relatively unproductive 

 of fish. It can readily be destroyed with the use of copper sulfate 

 at a rate not exceeding 1.0 p. p.m. Following destruction of musk- 

 grass, which is one of the dominant plants in hard waters of lime- 

 stone regions, microscopic plants or "water-bloom" algae often 

 follow the treatment, and thereafter they may be maintained by 

 fertilization. 



In mixing and applying copper sulfate, which is highly corrosive, 

 a galvanized tub, painted with asphalt varnish, a wooden tub, or a 

 crock may be used. Copper sulfate may be dissolved in a tub of 

 water and the chemical solution broadcast by hand from the front 

 end of a boat by use of a long-handled enameled dipper when treating 

 small ponds or water areas. Where pond scums are dense and cover a 

 good portion of the pond surface, it is desirable to use a sprayer 

 and pneumatic tank for a thorough application of copper sulfate in 

 the manner described on page 32 for distribution of sodium arsenite 

 solution. The use of brass or plastic fittings in the spraying 

 equipment will reduce corrosion. 



In treating surface scums with sodium arsenite, one gallon of 

 40 per cent sodium arsenite solution (4.0 pounds AS2O3 equivalent) 

 for each 16,020 cubic feet of the entire volume of water in a pond 

 may be used for effective control. 



Where the surface area is known in acres, or the body of water 

 to be treated is irregular and surface area is unknown, calcula- 

 tions may start from the area in acres, which may be determined by 

 methods previously described. The quantity of sodium arsenite 

 required may also be determined by this formula: 



Area in acres x average depth in feet x 2.7 x parts per million 

 required -i- 4 = gallons of sodium arsenite to use. 



As little as 2.5 p. p.m. will often give good control, but 4.0 

 p. p.m. is positive. It requires about 11.0 to 13.0 p. p.m. to kill 

 fish, but most bottom animals are destroyed by high rates of appli- 

 cation and the minimum quantity (usually 2.5 to 4 p. p.m.) needed 

 to control problem weeds should be used. Early treatments obviate 

 the need for using high treatment rates which may contaminate 



