Flourish Iron is a highly concentrated (10,000 mg/L) ferrous iron (Fe+2) gluconate supplement. It should be used in those cases where the iron requirements exceed that which can be delivered by Flourish at the recommended dose. Ferrous iron gluconate is a more suitable iron supplement for aquatic plants than is ferric (Fe+3) iron-EDTA for two reasons. (1) Plants require iron in the ferrous state, so physiological energy must be expended by the plant in order to extract the ferric iron from EDTA-iron and then convert (reduce) it to the ferrous form. Ferrous iron gluconate is already in the ferrous form so this reduction step is not necessary. (2) Ferrous gluconate is better suited to foliar feeding than is iron-EDTA owing to the relatively weaker iron-gluconate bonding vs. iron-EDTA bonding. Contains no phosphate or nitrate.