Most water quality parameters were in acceptable ranges for tilapia culture (Table 2). The TAN concentration spiked once to 8.55 mg/L in Trial 2 and once to 8.75 in Trial 4 for a short period (Figure 9). There was no observed mortality during these periods. Nitrite-nitrogen concentrations spiked once in each of Trials 1, 2 and 4. There was a peak concentration of NO2-N in Trial 1 of 13.62 mg/L, but this value was not included in the average (Table 2) because it was caused by mistakenly adding chlorinated water to replace evaporative losses. The chlorine appeared to affect Nitrobacterbacteria but not Nitrosomonas, as TAN levels did not increase during this period. In Trial 2 the peak NO2-N concentration of 18.27 followed the peak TAN concentration. In Trial 4 the peak NO2-N concentration of 13.58 mg/L coincided with the peak TAN concentration (Figures 9 and 10).