Bacterial abundance in each treatment was statistically different (p < 0.05). The abundance of bacteria in T3 was higher than in T1 and T2, from the beginning until the end of the experiment. Addition of commercial bacteria in T3 caused increasing bacterial population. The high bacterial density in T3 did not affect the high removal of inorganic nitrogen (especially NH3) if compared with T1 and T2. According to Tyson et al. (2008), operating optimal conditions for the biofiltration process, especially reconciling pH for ammonia, was more important than nitrifying bacteria population in system.