The nitrifying bacteria acting on various biofilter substrates including: scoria, P.V.C., marble and zeolite were evaluated. The experiment started with manufacture of a recirculation system with 130 liter fresh water volume in 7 l.min-1 flow rate in 3 replicate for every treatment. The volume of each biofilter was 60×40×30cm and after achievement to stable environmental conditions the nitrifying bacteria at a concentration of 105 ml-1were inoculated in each biofilters. Daily 3-10mg.l-1 of NH4Cl was added to biofilters. The procedure was conducted by exposure of Ammonium and Nitrate concentrations and pH in biofilters. The results showed that the Scoria can be reliable substrate as biofilter, in which provide the best substrate for the growth and attachment of the nitrifying bacteria which can reduce the retention time of a biofilter from 40-60 to 15 days