Tetra Plant Complete Substrate is a specially formulated substrate for creating an ideal environment for aquatic plants. It contains a blend of ingredients that provide long term fertilisation, and that support the development of beneficial micro-organisms. With no added nitrate or phosphate it does not encourage algae growth. How it Works TetraPlant Complete Substrate is rich in humic substances and nutrients. Humic substances encourage the development of beneficial micro-organisms that fix nutrients, making them more available to plants. In addition they complex nutrients in the water and substrate, making it easier for plants to absorb them. How to Use Add a 2cm deep layer of Complete Substrate to the base of the aquarium, and then cover with 2-3cm of aquarium gravel. We recommend gravel of 1-3mm diameter. Each tub (5kg) is sufficient for a 120 litre aquarium