72 MAINTAINING FISHES 



200 ml. of sample and mix. Final pH of sample should 

 be between 3.0 and 4.0. If a brown color results the 

 chlorine content of the sample is quite high. If a 

 brown color does not occur, add 1 ml. of starch solu- 

 tion. If a blue color is produced, a small but still dan- 

 gerous amount of chlorine is present. If no blue color 

 develops the sample is free of chlorine. 



ALTERNATE METHOD OF TESTING FOR CHLO- 

 RINE : The indicator orthotolidine is also widely used 

 for determining the presence of free chlorine. Use a 

 10 ml. sample and add 1 ml. of indicator. The pro- 

 duction of a yellow color demonstrates chlorine to be 

 present. 



Hydrogen Ion Activity 



Fishes tolerate a pH range of 5.0 to 9.0 with no 

 indications of difficulty. At greater extremes the mu- 

 cus covering of their bodies commences to coagulate 

 and mortality occurs. Most water has enough bufiFer- 

 ing ability to prevent the development of pH values 

 outside the safety range, but occasionally extremes 

 can occur and in some experimental work, such as 

 testing the toxicity of a chemical, careful pH control 

 is required. There are a number of satisfactory colori- 

 metric kits available which may be used for pH deter- 

 mination in connection with aquarium work. 



Alkalinity 



In aquarium work a measure of alkalinity is es- 

 sentially a measure of the carbonates. The carbonates 

 are of interest because of their ability to stabilize pH 

 and because variations in the carbonate content can 



