This is an excellent 12-page article applicable to Koi ponds or any recirculating system in which fish are kept.  See Outline of topics below...

System Operation
Particulates
Water Quality Management (excellent chart on the nitrogen cycle and the effects of fish waste on bacterial and chemical interactions)
   Temperature
   Dissolved oxygen
   Carbon dioxide (excellent chart on dissolved oxygen saturation at various temperatures)
   pH
   Nitrogen wastes (excellent charts on ammonia at various pH and temp, and another on alkalinity and aeration optimums)
        Pre-activation of biofilter
   Solids
   Chloride
Fish Management
   Stocking (excellent chart on water quality testing recommended values)
   Feeding (excellent chart on food consumption by fish weight)
        Feeding skills (excellent chart on stocking rates, fish weights, growth rate/period and feeding rates)
Stress & Disease Control
   Diseases (excellent chart on observed behavior, possible causes and possible management)
Conclusions (excellent chart on management options for water quality problems)

CLICK HERE to Read and/or download your copy.