Nano fibers in filter media have become increasingly interesting for filtration applications. The benefit of using nano fibers is the improvement with respect to filter efficiency and the relatively low pressure drop due to the nano slip. The cost of nano fibers and slow down in production process when using them leads to the desire to use as few nano fibers as possible. We treat such optimization issues by simulating filter media and filtration processes resolving the smallest scale. When considering the nano regime, two problems arise: The scales of the nano fibers and filter media thickness are very far apart, and the models for fluid flow and particle movement have to be extended by new physical effects like slip flow. The presentation gives an overview on the latest developments concerning nano filtration in Fraunhofer ITWMs software suite GeoDict / FilterDict.