THE AQUARIUM BUILDING I9 



Tlie latter is associated with the water's ability to 

 maintain a stable pH and especially to avoid drastic 

 drops of pH in unflushed tanks. At a methyl orange 

 alkalinity of less than 25 p.p.m., it is desirable to add 

 finely ground calcium carbonate to unflushed tanks. 



CARBON dioxide: Carbon dioxide frequently 

 occurs in well and spring water. Fishes commence to 

 exhibit effects of it at 50 p.p.m., and it is advisable to 

 maintain the concentration at a level below 30 p.p.m. 

 even though fishes can survive at higher concentra- 

 tions. The most efficient way to remove carbon diox- 

 ide is to spray the water into a louvered tower. It can 

 also be chemically removed with hydrated lime or tris- 

 hydro-xymethyl-aminomethane (for use of latter see 

 Chapters). 



iron: Iron, principally in the form of ferrous 

 bicarbonate, is a common contaminant of weU and 

 spring water. When this water first comes from the 

 ground, it is clear, but upon being aerated the ferrous 

 bicarbonate, at least in neutral and alkaline water, 

 forms a hydrated oxide in the form of a brown precipi- 

 tate. In the dissolved state, i.e., ferrous bicarbonate 

 form, iron is a mild irritant to fishes. The hydrated 

 oxide is not toxic but causes marked turbidity and 

 badly stains tanks and equipment. 



For low concentrations of iron (less than 5.0 p.p.m.) 

 and for limited water requirements (less than 1,000 

 gallons per day ) iron filters designed for home use are 

 quite satisfactory. These filters utilize manganese 

 zeohte which can be regenerated. For high concen- 

 trations of iron and for large quantities of water it is 



