Hi! Anthony, There is a lot of different forms of iron. While a little is needed in any system, too much of some types will lock up other minerals. If Tannin is present from the breakdown of some plant material, particularly Acacia bark as an example, Iron Tannate is formed which is a very stable material (Indian Ink), if this gets closely associated with minerals that are in short supply, they will get locked up in a form that soil biota and thence plants can not access. It is easy to mistake tannins with iron in water and often supposed iron is actually a mix.
If you find your iron rich water usable, go for it. You should grow great spinach and related veg. Gil
