Reactive transport modeling has become an important tool in geochemistry and has recently been expanded to isotopic studies as well. However, there is currently no publicly available code specifically tailored to isotopic studies. We therefore present here a computer program for 1-D reactive transport modeling of bacterially mediated isotope fractionation processes in porous media. Our numerical method allows the modeling of both stationary and time-dependent processes and implements various boundary condition types, including floating boundaries. The model specifically handles cases where the substrate is fully consumed, either at the lower boundary or at any point within the model. We provide a detailed analysis of our implementation as well as some example cases. The program is designed to be run on Matlab or Octave, which are available for all major operating systems.