For the Ni-system (ESI: Figure ), the evolution of the fitting parameters reflects a quick formation of µm-large particles preceded by a fast conversion of the short-lived amorphous phases t < 100 s (ESI: Figure ). Here, the crystallization of Ni-struvite was manifested itself in increasing G and Gsub values originated by the slope increase of the SAXS curves at low q near 0.1 nm -1 (affecting G) and the broad "hump" at around 0.4 nm -1 (affecting Gsub) (ESI: Figure ). After the formation of Ni-struvite crystals, all parameters reach a plateau value (ESI: Figure ). In contrast, in the Co-system (ESI: Figure ), the presence of persisting long-lived amorphous phases is manifesting itself by increasing G, Bsub, and Gsub values indicative of the presence of small building blocks and their agglomerates up to t = 500 s (ESI: Figure ). After t = 500 s these parameters decrease sharply, correlating with the development of diffraction reflections which correspond to Co-octahydrate. This suggests that the crystallization is driven by consumption of the amorphous phases. Indeed, we observed the co-existence of amorphous phases together with crystals in cryo-TEM analysis (Figure ). After around t = 600 s a plateau value is reached in most parameters, indicating the equilibration of the precipitation process.