A method for feeding reducing agent to an exhaust gas mass flow in an exhaust gas treatment device provides a reducing agent feed port, a storage catalytic converter storing reducing agent and an SCR catalytic converter for selective catalytic reduction of nitrogen oxygen compounds in exhaust gas. A first dosing strategy is followed, loading of the storage catalytic converter with reducing agent is monitored and a first target conversion rate is determined based on current loading. Reducing agent is fed according to the first target conversion rate. A current conversion rate obtained with the SCR catalytic converter is determined. The current conversion rate is compared to the first target conversion rate and any deviation is registered. A further dosing strategy, not considering the loading of the storage catalytic converter, is used if the deviation exceeds a first threshold value. A motor vehicle and a stationary installation are also provided.