Sodium is a minimalistically-essential nutrient that uses the power of osmosis.to assist with nutrient uptake. Sodium is the base of most traditional ag fertilizers. Sodium efficiency is extremely, extremely rare. A system can have next to no sodium and still run efficiently, but it’s technically considered a secondary nutrient because of the sheer amount of sodium that can be applied to the system without any problems. Sodium can assist (via the osmosis effect) in closing leaf stomatas. Excess sodium in a system WILL cause buildup; whether it be in your container, your reservoir, or your raised bed/field. This build up can affect the plant's ability to uptake other nutrients, as well as regulate water retention and control pH levels.