Flourish shows that Flourish is 0.32% iron. So, if you want 1 ppm, or 1 mg/liter of iron in the tank, add 1/.0032 mg of Flourish per liter of water, or about 300 mg (.3 grams) of Flourish per liter, which is 300 ml of Flourish per liter of water. Would somebody check this to see if I made a decimal mistake?