TREATMENT OF FISH-CULTURAL WATERS FOR REMOVAL OF ALG^. 879 

 I. DETERMINATION OF PROPORTION OF COPPER SULPHATE. 



It is first necessary to ascertain with a reasonable accuracy the amount of 

 copper sulphate required to kill the fish which are in the water that is to be 

 treated. Every species concerned should be tested. For this determination 

 it will be sufficient at the beginning to make the test for 24-hour periods in 

 standing water, with controls (i. e., extra or duplicate cans, of the same capacity, 

 containing the same quantity of water and the same number of fish, the only 

 difference between the two being that one holds copper sulphate dissolved in 

 the water and the other does not). Fish cans may in most cases be used as con- 

 tainers for the dilution in which the fish are placed and for the control. Any 

 receptacle large enough to hold a few individuals of the fish to be tested will 

 answer for this. A stock solution, from which to prepare the above dilutions, 

 should be made up in a glass bottle. 



The stock solution may be made holding 10 grams of copper sulphate per 

 liter of solution or, in other terms, approximately one-third of an avoirdupois 

 ounce, or 146 grains, of copper sulphate, with enough water added to make 

 I quart of solution, is a sufficient equivalent. Each cubic centimeter of this 

 solution will then contain 10 mg. of copper sulphate. If the test is to be 

 made with trout a test dilution of i to 1,000,000 may be made; that is, to 10 

 gallons (37,854 c. c, or 37,854,000 mg.) of water should be added 

 37,854,000-^1,000,000 = 37.8 mg. of copper sulphate, or 37.8 -h 10 =3.78 c. c. of 

 the stock solution. (The error in omitting to first remove 3.7 c. c. of water 

 from the 10 gallons is negligible.) This test dilution should be thoroughly 

 stirred. A few fishes should be introduced, not more than the water will 

 readily support for 24 hours or more without artificial aeration, as shown by 

 the control. The function of this extra or duplicate can or container, that of 

 checking the result, is obvious. After a certain amount of experience it may 

 be omitted. 



If the fishes all die in the test dilution while those in the control are alive, 

 a new trial should be made, using a weaker dilution. If they are all alive at the 

 end of 24 hours, a new trial should be made, using a stronger dilution. When 

 some of them live and some die during the 24 hours, the death point will have 

 been nearly fixed. The trials should be continued until it is ascertained what is 

 the strongest dilution of sulphate that may be used and yet leave all the fish 

 alive at the end of 24 hours. 



Having thus determined approximately the maximum amount of copper 

 sulphate that can be safely used, the treatment may be begun with somewhat 

 less than this amount. It is now necessary to determine the volume of water 

 flow which it is desired to treat. 



