Symmetries and skew-symmetries against onset of convection in porous layers salted from above and below

► Onset of convection in porous horizontal layer is studied. ► The layer is supposed to be salted from above and below. ► Guaranteeing global asymptotic stability of the conduction solution are obtained, for any value of the Prandtl salt numbers. ► A new methodology, based on the introduction of new fields and looking either for symmetries or for skew-symmetries, is introduced.