404 FISH HATCHERY MANAGEMENT 



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Figure G-1. A constant- flow device for dispensing liquid chemicals, (l) The de- 

 vice must be positioned over the water inflow to the fish-rearing unit, to insure 

 uniform mixing of the chemicals in the water. (2) The device can be made from 

 a conventional chicken waterer. Note siphon in place (arrow). 



volume into which the predetermined weight of chemical should be dis- 

 solved before treatment begins. 



If a 300-gallon tank were receiving a 10-gallon-per-minute water flow, 

 it would take at least 30 minutes (300 ^ 10) for water in the tank to be 

 replaced. It would take this long for any chemical to reach a desired 

 concentration in the tank. Thus, much of the treatment would be wast- 

 ed. To avoid such waste, it is best to pretreat the tank. The water flow 

 is shut off briefly, and chemical is quickly added to establish the final 

 concentration required (according to the formula for static treatment 

 above). Then the water flow is resumed and chemical metering is begun 

 with the constant-flow device. 



After all the chemical has been dispensed, some time will be required 

 for the last of it to be flushed from the treated tank. Partial draining of 

 the tank will flush much of the chemical from the unit. Fish should be 

 watched for signs of stress after, as well as during, the treatment period. 

 If effluent from the tank has to be treated for public- health reasons, such 

 treatment should be continued until all the chemical has disappeared 

 from the system. 



