I used the Fertilator to check the amount of Flourish Iron to be used in 130 gallons of water to achieve 0.10 ppm Fe. The Fertilator recommends 1 tsp. per 130 gal of water. The label on Flourish Iron recommends 1 tsp. (5ml) per 50 gal. of water to achieve the same result of 0.10 Fe. Which is the correct dosage.