I mixed Feso4 with 50% glutaraldehyde and 50% water and it turned from green to dark (red/brown) next day…. :0Both Are Ferrous
I am pretty-sure Seachem iron is ferrous, Fe2+. http://www.seachem.com/Products/product_pages/FlourishIron.html.
As I understand it (always dangerous ), ferrous iron, Fe2+ is the directly usable form, for plants. The problem is Fe2+ is also less stable, needs to be dosed more frequently and is more likely to be adversely affected by water conditions, alkalinity in particular.
I know there have been some good discussions around here on the subject.