API Root Tabs is a superior plant fertilizer in tablet form. Contains key essential nutrients to stimulate lush plant growth. Gets new plants off to a good start and keeps established plants flourishing. Benefits: Aquarium plants require certain essential nutrients for vibrant growth. Root tabs are formulated to supply key nutrients, including iron and potassium, to help new aquatic plants get off to a vigorous start and keep established plants flourishing. Directions: Add 1 tablet for each 30 sq inches of gravel surface. Add new tablets monthly.Rich in iron Promotes strong root development Long-lasting formula -- feeds plants for a month Use in freshwater aquariums Will not harm fish