A process is provided for fermenting CO-containing gaseous substrates in a low phosphate medium. The process includes blending a liquid medium that includes at least one transition metal element with a liquid medium that includes at least at least one other transition metal element and one non-metal element to provide a fermentation medium. The process is effective for preventing precipitation of one or more transition metal elements with one or more non-metal elements. The fermentation medium used in the process is prepared in a way that requires significantly lower amounts of water and reduced levels of phosphate.