n tropical streambeds, aquatic plants are found growing in a special clay called Laterite. FIRST LAYER is an all natural Laterite in a granular form, which is ideal for aquarium use. The pure Laterite in FIRST LAYER provides the perfect planting medium for a natural aquarium. Mixing all natural Laterite into the gravel bed creates an excellent planting medium for rooted aquatic plants. Safe for use with tropical fish.