Iron is one of the most important micronutrients in the nutrient food web. Very much like Calcium, it has a plethora of antagonistic relationships in soils and root systems. When it is out of balance it can cause a plethora of issues including chlorosis. This chlorosis is comes from the fact that iron is a necessary element in the formation of chlorophyll. It is also responsible for other processes within the plant because it is a constituent of many different enzymes and pigments. In EDTA form, iron is efficiently bioavailable so it can be used in nutrient systems of all kinds. One of the double-edged sword properties of iron is that it is very pH dependent. This means that when your start seeing an iron deficiency, more often than not, there is an issue with pH in your soil or reservoir system.