There is no reason to add Fe in that tank.Ms Walstad mentions in her book that available iron in the tank water can be a cause of algae growths. Algae has no access to any iron that is in the substrate, and they need iron to grow. I think I can test that idea using my 10 gallon tank, with a barrier in the middle, making it two 5 gallon, independent, tanks, each with the same light, the same substrate, and nearly identical plants. To do this I will start dosing Flourish Iron in only one of the two tanks. I would expect to see noticeable algae start growing in the tank with the iron. Today I dosed one tank with the 0.5 ml dosage per the Seachem recommendation. Both tanks get NPK and trace elements, including iron, every other day.
The iron is dosed in the left hand tank.