Seachem Flourish Iron 500ml (17 fl.oz) is a highly concentrated (10,000mg-L) iron gluconate supplement. It should be used if the requirements for iron exceed those that Flourish provide at the recommended dose. Once dosed the iron is maintained in the ferrous (fe+2) state for an extended period due to the polygluconate complexation which allows the plants to use the iron far easier than from EDTA sources