Bioavailable Ferrous & Ferric Iron Source for all Planted Aquaria. Provides both ferrous (Fe2+) and ferric (Fe3+) iron sources to maximize benefit to planted aquaria. Two-tiered approach to iron supplementation consists of one ingredient to deliver immediate iron and another ingredient that slowly releases iron during the light cycle, when the aquarium is illuminated. Over 50% stronger than most competing products. Formulated utilizing extensive research on aquatic plant nutrient requirements.