Photodarkening and photobleaching effects in case of UV-femtosecond-pulse exposure of optical fibres are investigated. We evaluate the existence of loss equilibrium states in Yb-doped and Yb-free fibres. Supposing that parasitic VIS to NIR losses induced by fibre Bragg grating (FBG) inscription can also be addressed by a photobleaching treatment, we find grating absorption remarkably reduced by a post-exposure treatment. We also present photobleaching applied directly after FBG inscription with UV-femtosecond pulses to improve the wavelength and power stability of a monolithic FBG-based fibre laser as a noteworthy alternative to subsequent thermal treatment.