20 MAINTAINING FISHES 



necessary to aerate the water and then remove the 

 precipitated iron by employing a sand filter. 



SODIUM chloride: Sodium chloride some- 

 times occm's in well water. There is no satisfactory 

 means of removing sodium chloride on a large enough 

 scale practical for aquarium use. Fortunately it is not 

 highly toxic to most fishes, but its presence makes the 

 water imsuited for some types of experimental work. 



HYDROGEN SULFIDE: Hydrogen sulfide occurs 

 in well water of some areas. It is highly toxic to fishes 

 and its removal is usually not practical. 



INDUSTRIAL POLLUTANTS: Industrial pollut- 

 ants are of particular concern when a stream is uti- 

 lized as a water supply. There are a great number of 

 industrial pollutants many of which cannot be satis- 

 factorily removed. It is not practical to deal with them 

 in the present work. 



CHLORINE : Chlorine is a serious pollutant of tap 

 water. It may be removed by heating, aging, chemi- 

 cal treatment, or charcoal filtration. The latter method 

 is superior to all others. Small, highly successful char- 

 coal filters can be purchased for approximately 

 $100.00. They may also be built since they consist of 

 nothing more than a column of animal charcoal (ap- 

 proximately /8 inch particle size) through which wa- 

 ter flows at a reduced rate. 



Removal of chlorine by heating requires that the 

 water be held at approximately 180° F. for at least 

 thirty minutes. Removal by aging requires from four 



