A chemical erosion study of pyrolytic graphite under low-energy deuterium ion impact for cases of H and D atom wall conditioning was performed. The QMS signal amplitudes and erosion yield magnitudes obtained for the two conditioning cases were compared at energies of 50, 100, and 200eV/D + over a temperature range of 500--900K. Comparing QMS signal amplitudes for the two conditioning cases indicated that the species on the wall does affect the molecules detected through RGA, although, this could not be fully quantified due to experimental uncertainty which was primarily caused by the presence of water in the test chamber. In comparing the erosion yield magnitudes, we see reductions in the maximum total chemical erosion yield (Ymax) for H conditioning compared to D conditioning by factors of ∼1.9, 1.7, and 1.2 at 50, 100, and 200eV/D+, respectively.