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 or signs of iron deficiency appear (such as short and slender stems or yellowing between veins.) Plants are able to much more easily derive a benefit from Flourish Iron™ than from EDTA-iron sources because all EDTA iron is in the ferric (Fe+3) state. Since plants require iron in the ferrous state, additional physiological energy must be expended in order to extract the ferric iron from EDTA-iron and then convert it to the ferrous form. Contains no phosphate or nitrate. DIRECTIONS: Use 1 capful (5 mL) for each 200 L (50 gallons*) or as required to maintain about 0.10 mg/L iron. For smaller doses please note that each cap thread is about 1 mL. Use MultiTest: Iron™ test kit to monitor iron concentrations. Use as needed to combat signs of iron deficiency (usually seen in new growth) which include: chlorosis (yellowing) of tissue between veins and short and slender stems.