A system and method for determining when to provide an anode exhaust gas bleed from a fuel cell stack as the fuel cell stack ages. The method determines the amount of nitrogen flowing from a cathode side to an anode side of the fuel cell stack. The method also determines the amount of nitrogen flowing from the anode side to the cathode side by determining a standard deviation of voltage outputs of the fuel cells, and using the standard deviation as a model for determining the leak rate of nitrogen from the anode side to the cathode side. The method determines the concentration of nitrogen in the anode side based on the nitrogen flow between the cathode and anode side, and opens a bleed valve to bleed the anode exhaust gas if the concentration of nitrogen in the anode side goes above a predetermined value.