This study compares the behavior of nitrification (NH4+, NO2- and NO3-), and performance, in terms of the surface TAN conversion rate (STR), volumetric TAN conversion rate (VTR) and removal percentage of TAN (PTR) among three fixation media of nitrifying bacteria (two alternatives (S1, S2) and one commercial (Co)). The experiment was performed in two tests of 42 days each. Three isolated biofiltration systems were built for the experience, to which were added media colonized by bacteria as a "seed" to start the process of nitrification. Ammonium chloride (NH4Cl) was attached as source of ammonium in reconditioned freshwater, also gradually adding inorganic carbon (HCO3-) to maintain moderate water hardness. The average results for both tests indicate that the substrates S1 and S2 show a statistically similar behavior to the substrate Co (P > 0.05) during the first 33 days (until steady state). For the second test in terms of performance, STR values were 0.40, 0.39, 0.39 g TAN m-2 d-1 recorded for S2 and Co respectively; in terms of PRN, values were 92(3) 9־/ and 93% for S1, S2 and Co, respectively. Regarding VTR, values of 72.31, 114.94, and 39.02 g TAN m-3 d-1 were recorded for S2 and Co respectively. Statistical analysis provided that for STR and PRN, no significant differences, were found. But for VTR, statistically significant differences between means were evaluated, registering for the S2 media the highest value of VTR.