Two separate recirculating systems were configured to maintain fish in water with low or moderate hardness for concurrent 8-week feeding trials using the same diets. The water source was dechlorinated municipal water, which is consistently low in hardness. Each recirculating system contained eight 110-L glass aquaria, a 93.25-watt pump, a 4180-L reservoir containing plastic biospheres to act as a biofilter, and a 1000-watt heater to maintain the temperature