Highly concentrated iron for planted aquariums. The best form of iron for absorption through the leaves. Prevents leaf yellowing. Flourish Iron is a highly concentrated iron gluconate supplement. It is suitable as an iron supplement when the supply of Flourish is insufficient. Thanks to its formula, Flourish Iron remains in its iron form (Fe2+) for a long time after being added to the aquarium, unlike formulas in the form of iron(III), which must be converted by the plant at the roots to benefit all parts of the plant. This assimilation process requires energy and thus leads to a loss of plant growth. 4 liters treat 240,000 liters.