  We present the transverse momentum spectra and rapidity distributions of
$\pi^{-}$ and K$^0_S$ in Ar+KCl reactions at a beam kinetic energy of 1.756 A
GeV measured with the spectrometer HADES. The reconstructed K$^0_S$ sample is
characterized by good event statistics for a wide range in momentum and
rapidity. We compare the experimental $\pi^{-}$ and K$^0_S$ distributions to
predictions by the IQMD model. The model calculations show that K$^0_S$ at low
tranverse momenta constitute a particularly well suited tool to investigate the
kaon in-medium potential. Our K$^0_S$ data suggest a strong repulsive in-medium
K$^0$ potential of about 40 MeV strength.
