PLANT SUBSTRATE acts as a long term nutrition store for waterplants, so ensuring magnificent and healthy waterplant growth. PLANT SUBSTRATE is a natural concentrate of clay and sphagnum, laid at the bottom of the gravel layer when you build your aquarium. Clay and sphagnum slowly release nutrients to waterplant roots and binds nutrition in the water in the bottom layer. Removing nutrition from water reduces the risk of undesirable algae growth.