First, we discuss the possibility of explaining the 3.5 keV line through dark matter decaying to axion-like particles that subsequently convert to photons in astrophysical magnetic fields. This model is consistent with all present observations of the 3.5 keV line, including galaxy clusters, spiral and dwarf galaxies and the galactic centre. Then, we discuss how a Cosmic-ALP-background can explain the excess of Soft X-rays in galaxy clusters.